diff --git a/packages/Avalonia/Avalonia.csproj b/packages/Avalonia/Avalonia.csproj
index af9ed71c5f..4b28527465 100644
--- a/packages/Avalonia/Avalonia.csproj
+++ b/packages/Avalonia/Avalonia.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-      <TargetFrameworks>netstandard2.0;net461;netcoreapp2.0;net6.0</TargetFrameworks>
+      <TargetFrameworks>net6.0;netstandard2.0;net461;netcoreapp2.0</TargetFrameworks>
       <PackageId>Avalonia</PackageId>
   </PropertyGroup>
 
diff --git a/readme.md b/readme.md
index a8a6399f2f..b38552a010 100644
--- a/readme.md
+++ b/readme.md
@@ -75,6 +75,12 @@ For more information see the [.NET Foundation Code of Conduct](https://dotnetfou
 
 Avalonia is licenced under the [MIT licence](licence.md).
 
+## Support Avalonia
+
+**BTC**: bc1q05wx78qemgy9x6ytl5ljk2xrt00yqargyjm8gx
+
+This will be shared with the community and awarded for significant contributions.
+
 ### Backers
 
 Thank you to all our backers! 🙏 [[Become a backer](https://opencollective.com/Avalonia#backer)]
diff --git a/samples/ControlCatalog.Android/ControlCatalog.Android.csproj b/samples/ControlCatalog.Android/ControlCatalog.Android.csproj
index 1a68c4d732..617b6b6ab0 100644
--- a/samples/ControlCatalog.Android/ControlCatalog.Android.csproj
+++ b/samples/ControlCatalog.Android/ControlCatalog.Android.csproj
@@ -32,7 +32,7 @@
     <EmbedAssembliesIntoApk>True</EmbedAssembliesIntoApk>
     <BundleAssemblies>False</BundleAssemblies>
     <AndroidCreatePackagePerAbi>False</AndroidCreatePackagePerAbi>
-    <AndroidSupportedAbis>armeabi-v7a;x86</AndroidSupportedAbis>
+    <AndroidSupportedAbis>armeabi-v7a;x86;x86_64</AndroidSupportedAbis>
     <Debugger>Xamarin</Debugger>
     <AndroidEnableMultiDex>False</AndroidEnableMultiDex>
     <AotAssemblies>False</AotAssemblies>
@@ -51,7 +51,7 @@
     <EmbedAssembliesIntoApk>True</EmbedAssembliesIntoApk>
     <BundleAssemblies>False</BundleAssemblies>
     <AndroidCreatePackagePerAbi>False</AndroidCreatePackagePerAbi>
-    <AndroidSupportedAbis>armeabi-v7a,x86</AndroidSupportedAbis>
+    <AndroidSupportedAbis>armeabi-v7a,x86;x86_64</AndroidSupportedAbis>
     <Debugger>Xamarin</Debugger>
     <AotAssemblies>False</AotAssemblies>
     <EnableLLVM>False</EnableLLVM>
@@ -125,6 +125,10 @@
       <Project>{42472427-4774-4c81-8aff-9f27b8e31721}</Project>
       <Name>Avalonia.Layout</Name>
     </ProjectReference>
+    <ProjectReference Include="..\..\src\Avalonia.Themes.Fluent\Avalonia.Themes.Fluent.csproj">
+      <Project>{c42d2fc1-a531-4ed4-84b9-89aec7c962fc}</Project>
+      <Name>Avalonia.Themes.Fluent</Name>
+    </ProjectReference>
     <ProjectReference Include="..\..\src\Avalonia.Visuals\Avalonia.Visuals.csproj">
       <Project>{eb582467-6abb-43a1-b052-e981ba910e3a}</Project>
       <Name>Avalonia.Visuals</Name>
diff --git a/src/Android/Avalonia.Android/AndroidPlatform.cs b/src/Android/Avalonia.Android/AndroidPlatform.cs
index 5e11d8eab2..57f22e7a05 100644
--- a/src/Android/Avalonia.Android/AndroidPlatform.cs
+++ b/src/Android/Avalonia.Android/AndroidPlatform.cs
@@ -43,11 +43,12 @@ namespace Avalonia.Android
             AvaloniaLocator.CurrentMutable
                 .Bind<IClipboard>().ToTransient<ClipboardImpl>()
                 .Bind<ICursorFactory>().ToTransient<CursorFactory>()
+                .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformStub())
                 .Bind<IKeyboardDevice>().ToSingleton<AndroidKeyboardDevice>()
                 .Bind<IPlatformSettings>().ToConstant(Instance)
                 .Bind<IPlatformThreadingInterface>().ToConstant(new AndroidThreadingInterface())
                 .Bind<ISystemDialogImpl>().ToTransient<SystemDialogImpl>()
-                .Bind<IPlatformIconLoader>().ToSingleton<PlatformIconLoader>()
+                .Bind<IPlatformIconLoader>().ToSingleton<PlatformIconLoaderStub>()
                 .Bind<IRenderTimer>().ToConstant(new ChoreographerTimer())
                 .Bind<IRenderLoop>().ToConstant(new RenderLoop())
                 .Bind<PlatformHotkeyConfiguration>().ToSingleton<PlatformHotkeyConfiguration>()
diff --git a/src/Android/Avalonia.Android/Stubs.cs b/src/Android/Avalonia.Android/Stubs.cs
new file mode 100644
index 0000000000..f36c01dbc8
--- /dev/null
+++ b/src/Android/Avalonia.Android/Stubs.cs
@@ -0,0 +1,56 @@
+using System;
+using System.IO;
+using Avalonia.Platform;
+
+namespace Avalonia.Android
+{
+    class WindowingPlatformStub : IWindowingPlatform
+    {
+        public IWindowImpl CreateWindow() => throw new NotSupportedException();
+
+        public IWindowImpl CreateEmbeddableWindow() => throw new NotSupportedException();
+
+        public ITrayIconImpl CreateTrayIcon() => null;
+    }
+
+    class PlatformIconLoaderStub : IPlatformIconLoader
+    {
+        public IWindowIconImpl LoadIcon(IBitmapImpl bitmap)
+        {
+            using (var stream = new MemoryStream())
+            {
+                bitmap.Save(stream);
+                return LoadIcon(stream);
+            }
+        }
+
+        public IWindowIconImpl LoadIcon(Stream stream)
+        {
+            var ms = new MemoryStream();
+            stream.CopyTo(ms);
+            return new IconStub(ms);
+        }
+
+        public IWindowIconImpl LoadIcon(string fileName)
+        {
+            using (var file = File.Open(fileName, FileMode.Open))
+                return LoadIcon(file);
+        }
+    }
+
+    public class IconStub : IWindowIconImpl
+    {
+        private readonly MemoryStream _ms;
+
+        public IconStub(MemoryStream stream)
+        {
+            _ms = stream;
+        }
+
+        public void Save(Stream outputStream)
+        {
+            _ms.Position = 0;
+            _ms.CopyTo(outputStream);
+        }
+    }
+}
diff --git a/src/Android/Avalonia.AndroidTestApplication/Resources/Resource.Designer.cs b/src/Android/Avalonia.AndroidTestApplication/Resources/Resource.Designer.cs
index 83db67fcee..87fd47df25 100644
--- a/src/Android/Avalonia.AndroidTestApplication/Resources/Resource.Designer.cs
+++ b/src/Android/Avalonia.AndroidTestApplication/Resources/Resource.Designer.cs
@@ -14,7 +14,7 @@ namespace Avalonia.AndroidTestApplication
 {
 	
 	
-	[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Xamarin.Android.Build.Tasks", "1.0.0.0")]
+	[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Xamarin.Android.Build.Tasks", "12.1.99.62")]
 	public partial class Resource
 	{
 		
diff --git a/src/Avalonia.Animation/Avalonia.Animation.csproj b/src/Avalonia.Animation/Avalonia.Animation.csproj
index 85938ad958..465b922b72 100644
--- a/src/Avalonia.Animation/Avalonia.Animation.csproj
+++ b/src/Avalonia.Animation/Avalonia.Animation.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />
diff --git a/src/Avalonia.Base/Avalonia.Base.csproj b/src/Avalonia.Base/Avalonia.Base.csproj
index 07614f31db..376075df2a 100644
--- a/src/Avalonia.Base/Avalonia.Base.csproj
+++ b/src/Avalonia.Base/Avalonia.Base.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <AssemblyName>Avalonia.Base</AssemblyName>
     <RootNamespace>Avalonia</RootNamespace>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>    
diff --git a/src/Avalonia.Base/AvaloniaLocator.cs b/src/Avalonia.Base/AvaloniaLocator.cs
index 0510852ea7..8ec245507b 100644
--- a/src/Avalonia.Base/AvaloniaLocator.cs
+++ b/src/Avalonia.Base/AvaloniaLocator.cs
@@ -125,6 +125,16 @@ namespace Avalonia
         {
             return (T?) resolver.GetService(typeof (T));
         }
+
+        public static object GetRequiredService(this IAvaloniaDependencyResolver resolver, Type t)
+        {
+            return resolver.GetService(t) ?? throw new InvalidOperationException($"Unable to locate '{t}'.");
+        }
+
+        public static T GetRequiredService<T>(this IAvaloniaDependencyResolver resolver)
+        {
+            return (T?)resolver.GetService(typeof(T)) ?? throw new InvalidOperationException($"Unable to locate '{typeof(T)}'.");
+        }
     }
 }
 
diff --git a/src/Avalonia.Base/Threading/Dispatcher.cs b/src/Avalonia.Base/Threading/Dispatcher.cs
index 949c11fbe0..ffc013268d 100644
--- a/src/Avalonia.Base/Threading/Dispatcher.cs
+++ b/src/Avalonia.Base/Threading/Dispatcher.cs
@@ -56,11 +56,7 @@ namespace Avalonia.Threading
         /// </param>
         public void MainLoop(CancellationToken cancellationToken)
         {
-            var platform = AvaloniaLocator.Current.GetService<IPlatformThreadingInterface>();
-
-            if (platform is null)
-                throw new InvalidOperationException("Unable to locate IPlatformThreadingInterface");
-
+            var platform = AvaloniaLocator.Current.GetRequiredService<IPlatformThreadingInterface>();
             cancellationToken.Register(() => platform.Signal(DispatcherPriority.Send));
             platform.RunLoop(cancellationToken);
         }
diff --git a/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs b/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs
index 66223e513d..88b1e3c807 100644
--- a/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs
+++ b/src/Avalonia.Base/Utilities/WeakSubscriptionManager.cs
@@ -180,7 +180,7 @@ namespace Avalonia.Utilities
                 {
                     var r = _data[c];
                     if (r?.TryGetTarget(out var sub) == true)
-                        sub.OnEvent(sender, eventArgs);
+                        sub!.OnEvent(sender, eventArgs);
                     else
                         needCompact = true;
                 }
diff --git a/src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj b/src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj
index 7884f13ddb..e864ea2007 100644
--- a/src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj
+++ b/src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj
@@ -6,7 +6,7 @@
         <BuildOutputTargetFolder>tools</BuildOutputTargetFolder>
         <DefineConstants>$(DefineConstants);BUILDTASK;XAMLX_CECIL_INTERNAL;XAMLX_INTERNAL</DefineConstants>
         <CopyLocalLockFileAssemblies Condition="$(TargetFramework) == 'netstandard2.0'">true</CopyLocalLockFileAssemblies>
-        <NoWarn>NU1605</NoWarn>
+        <NoWarn>NU1605;CS8632</NoWarn>
     </PropertyGroup>
 
     <ItemGroup>
diff --git a/src/Avalonia.Controls.DataGrid/Avalonia.Controls.DataGrid.csproj b/src/Avalonia.Controls.DataGrid/Avalonia.Controls.DataGrid.csproj
index d50e8b1115..c89157dc0f 100644
--- a/src/Avalonia.Controls.DataGrid/Avalonia.Controls.DataGrid.csproj
+++ b/src/Avalonia.Controls.DataGrid/Avalonia.Controls.DataGrid.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <PackageId>Avalonia.Controls.DataGrid</PackageId>
   </PropertyGroup>
   <ItemGroup>
diff --git a/src/Avalonia.Controls/Avalonia.Controls.csproj b/src/Avalonia.Controls/Avalonia.Controls.csproj
index 479bbb49b6..e2c6a714aa 100644
--- a/src/Avalonia.Controls/Avalonia.Controls.csproj
+++ b/src/Avalonia.Controls/Avalonia.Controls.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="..\Avalonia.Base\Metadata\NullableAttributes.cs" Link="NullableAttributes.cs" />
diff --git a/src/Avalonia.Controls/Button.cs b/src/Avalonia.Controls/Button.cs
index 8b22cdd4ec..8537c9acbc 100644
--- a/src/Avalonia.Controls/Button.cs
+++ b/src/Avalonia.Controls/Button.cs
@@ -304,15 +304,18 @@ namespace Avalonia.Controls
         /// </summary>
         protected virtual void OnClick()
         {
-            OpenFlyout();
+            if (IsEffectivelyEnabled)
+            {
+                OpenFlyout();
 
-            var e = new RoutedEventArgs(ClickEvent);
-            RaiseEvent(e);
+                var e = new RoutedEventArgs(ClickEvent);
+                RaiseEvent(e);
 
-            if (!e.Handled && Command?.CanExecute(CommandParameter) == true)
-            {
-                Command.Execute(CommandParameter);
-                e.Handled = true;
+                if (!e.Handled && Command?.CanExecute(CommandParameter) == true)
+                {
+                    Command.Execute(CommandParameter);
+                    e.Handled = true;
+                }
             }
         }
 
diff --git a/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs b/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
index af3fdbd662..a856ee071c 100644
--- a/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
+++ b/src/Avalonia.Controls/Calendar/CalendarDatePicker.cs
@@ -1,4 +1,4 @@
-// (c) Copyright Microsoft Corporation.
+// (c) Copyright Microsoft Corporation.
 // This source is subject to the Microsoft Public License (Ms-PL).
 // Please see http://go.microsoft.com/fwlink/?LinkID=131993 for details.
 // All other rights reserved.
@@ -425,9 +425,6 @@ namespace Avalonia.Controls
         {
             FocusableProperty.OverrideDefaultValue<CalendarDatePicker>(true);
 
-            DisplayDateProperty.Changed.AddClassHandler<CalendarDatePicker>((x,e) => x.OnDisplayDateChanged(e));
-            DisplayDateStartProperty.Changed.AddClassHandler<CalendarDatePicker>((x,e) => x.OnDisplayDateStartChanged(e));
-            DisplayDateEndProperty.Changed.AddClassHandler<CalendarDatePicker>((x,e) => x.OnDisplayDateEndChanged(e));
             IsDropDownOpenProperty.Changed.AddClassHandler<CalendarDatePicker>((x,e) => x.OnIsDropDownOpenChanged(e));
             SelectedDateProperty.Changed.AddClassHandler<CalendarDatePicker>((x,e) => x.OnSelectedDateChanged(e));
             SelectedDateFormatProperty.Changed.AddClassHandler<CalendarDatePicker>((x,e) => x.OnSelectedDateFormatChanged(e));
@@ -459,18 +456,12 @@ namespace Avalonia.Controls
             if (_calendar != null)
             {
                 _calendar.SelectionMode = CalendarSelectionMode.SingleDate;
-                _calendar.SelectedDate = SelectedDate;
-                SetCalendarDisplayDate(DisplayDate);
-                SetCalendarDisplayDateStart(DisplayDateStart);
-                SetCalendarDisplayDateEnd(DisplayDateEnd);
 
                 _calendar.DayButtonMouseUp += Calendar_DayButtonMouseUp;
                 _calendar.DisplayDateChanged += Calendar_DisplayDateChanged;
                 _calendar.SelectedDatesChanged += Calendar_SelectedDatesChanged;
                 _calendar.PointerReleased += Calendar_PointerReleased;
                 _calendar.KeyDown += Calendar_KeyDown;
-                //_calendar.SizeChanged += new SizeChangedEventHandler(Calendar_SizeChanged);
-                //_calendar.IsTabStop = true;
 
                 var currentBlackoutDays = BlackoutDates;
                 BlackoutDates = _calendar.BlackoutDates;
@@ -587,58 +578,6 @@ namespace Avalonia.Controls
             SetSelectedDate();
         }
         
-        private void SetCalendarDisplayDate(DateTime value)
-        {
-            if (DateTimeHelper.CompareYearMonth(_calendar.DisplayDate, value) != 0)
-            {
-                _calendar.DisplayDate = DisplayDate;
-                if (DateTime.Compare(_calendar.DisplayDate, DisplayDate) != 0)
-                {
-                    DisplayDate = _calendar.DisplayDate;
-                }
-            }
-        }
-        private void OnDisplayDateChanged(AvaloniaPropertyChangedEventArgs e)
-        {
-            if (_calendar != null)
-            {
-                var value = (DateTime)e.NewValue;
-                SetCalendarDisplayDate(value);
-            }
-        }
-        private void SetCalendarDisplayDateStart(DateTime? value)
-        {
-            _calendar.DisplayDateStart = value;
-            if (_calendar.DisplayDateStart.HasValue && DisplayDateStart.HasValue && DateTime.Compare(_calendar.DisplayDateStart.Value, DisplayDateStart.Value) != 0)
-            {
-                DisplayDateStart = _calendar.DisplayDateStart;
-            }
-        }
-        private void OnDisplayDateStartChanged(AvaloniaPropertyChangedEventArgs e)
-        {
-            if (_calendar != null)
-            {
-                var value = (DateTime?)e.NewValue;
-                SetCalendarDisplayDateStart(value);
-            }
-        }
-        private void SetCalendarDisplayDateEnd(DateTime? value)
-        {
-            _calendar.DisplayDateEnd = value;
-            if (_calendar.DisplayDateEnd.HasValue && DisplayDateEnd.HasValue && DateTime.Compare(_calendar.DisplayDateEnd.Value, DisplayDateEnd.Value) != 0)
-            {
-                DisplayDateEnd = _calendar.DisplayDateEnd;
-            }
-
-        }
-        private void OnDisplayDateEndChanged(AvaloniaPropertyChangedEventArgs e)
-        {
-            if (_calendar != null)
-            {
-                var value = (DateTime?)e.NewValue;
-                SetCalendarDisplayDateEnd(value);
-            }
-        }
         private void OnIsDropDownOpenChanged(AvaloniaPropertyChangedEventArgs e)
         {
             var oldValue = (bool)e.OldValue;
@@ -670,11 +609,6 @@ namespace Avalonia.Controls
             var addedDate = (DateTime?)e.NewValue;
             var removedDate = (DateTime?)e.OldValue;
 
-            if (_calendar != null && addedDate != _calendar.SelectedDate)
-            {
-                _calendar.SelectedDate = addedDate;
-            }
-
             if (SelectedDate != null)
             {
                 DateTime day = SelectedDate.Value;
diff --git a/src/Avalonia.Controls/Grid.cs b/src/Avalonia.Controls/Grid.cs
index 4e60b52f83..74401c450a 100644
--- a/src/Avalonia.Controls/Grid.cs
+++ b/src/Avalonia.Controls/Grid.cs
@@ -978,7 +978,7 @@ namespace Avalonia.Controls
         /// width is not registered in columns.</param>
         /// <param name="forceInfinityV">Passed through to MeasureCell.
         /// When "true" cells' desired height is not registered in rows.</param>
-        /// <param name="hasDesiredSizeUChanged">return true when desired size has changed</param>
+        /// <param name="hasDesiredSizeUChanged">When the method exits, indicates whether the desired size has changed.</param>
         private void MeasureCellsGroup(
             int cellsHead,
             Size referenceSize,
diff --git a/src/Avalonia.Controls/SystemDialog.cs b/src/Avalonia.Controls/SystemDialog.cs
index 3fac10b2d1..3487f427d7 100644
--- a/src/Avalonia.Controls/SystemDialog.cs
+++ b/src/Avalonia.Controls/SystemDialog.cs
@@ -66,8 +66,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            var service = AvaloniaLocator.Current.GetService<ISystemDialogImpl>() ??
-                throw new InvalidOperationException("Unable to locate ISystemDialogImpl.");
+            var service = AvaloniaLocator.Current.GetRequiredService<ISystemDialogImpl>();
             return (await service.ShowFileDialogAsync(this, parent) ??
              Array.Empty<string>()).FirstOrDefault();
         }
@@ -95,8 +94,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            var service = AvaloniaLocator.Current.GetService<ISystemDialogImpl>() ??
-                throw new InvalidOperationException("Unable to locate ISystemDialogImpl.");
+            var service = AvaloniaLocator.Current.GetRequiredService<ISystemDialogImpl>();
             return service.ShowFileDialogAsync(this, parent);
         }
     }
@@ -125,8 +123,7 @@ namespace Avalonia.Controls
         {
             if(parent == null)
                 throw new ArgumentNullException(nameof(parent));
-            var service = AvaloniaLocator.Current.GetService<ISystemDialogImpl>() ??
-                throw new InvalidOperationException("Unable to locate ISystemDialogImpl.");
+            var service = AvaloniaLocator.Current.GetRequiredService<ISystemDialogImpl>();
             return service.ShowFolderDialogAsync(this, parent);
         }
     }
diff --git a/src/Avalonia.DesignerSupport/Avalonia.DesignerSupport.csproj b/src/Avalonia.DesignerSupport/Avalonia.DesignerSupport.csproj
index 9d8842f613..f8a7cdc690 100644
--- a/src/Avalonia.DesignerSupport/Avalonia.DesignerSupport.csproj
+++ b/src/Avalonia.DesignerSupport/Avalonia.DesignerSupport.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <!-- WARNING! The designer support version number needs to be frozen 
          To allow projects that implement designer functionality to still
          work with newer versions of Avalonia. This version number only
diff --git a/src/Avalonia.Desktop/Avalonia.Desktop.csproj b/src/Avalonia.Desktop/Avalonia.Desktop.csproj
index 114e6d7abd..d423aa7dae 100644
--- a/src/Avalonia.Desktop/Avalonia.Desktop.csproj
+++ b/src/Avalonia.Desktop/Avalonia.Desktop.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-      <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+      <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
       <PackageId>Avalonia.Desktop</PackageId>
   </PropertyGroup>
 
diff --git a/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj b/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj
index 29a8e05cfa..f2a0faeb22 100644
--- a/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj
+++ b/src/Avalonia.DesktopRuntime/Avalonia.DesktopRuntime.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net461;netcoreapp2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;net461;netcoreapp2.0</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Avalonia.Diagnostics/Avalonia.Diagnostics.csproj b/src/Avalonia.Diagnostics/Avalonia.Diagnostics.csproj
index 871821dd70..1fc3604f70 100644
--- a/src/Avalonia.Diagnostics/Avalonia.Diagnostics.csproj
+++ b/src/Avalonia.Diagnostics/Avalonia.Diagnostics.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <RootNamespace>Avalonia</RootNamespace>
     <PackageId>Avalonia.Diagnostics</PackageId>
   </PropertyGroup>
diff --git a/src/Avalonia.Diagnostics/Diagnostics/ViewModels/TreePageViewModel.cs b/src/Avalonia.Diagnostics/Diagnostics/ViewModels/TreePageViewModel.cs
index 27b28f35fc..4416437479 100644
--- a/src/Avalonia.Diagnostics/Diagnostics/ViewModels/TreePageViewModel.cs
+++ b/src/Avalonia.Diagnostics/Diagnostics/ViewModels/TreePageViewModel.cs
@@ -86,14 +86,15 @@ namespace Avalonia.Diagnostics.ViewModels
         public void SelectControl(IControl control)
         {
             var node = default(TreeNode);
+            IControl? c = control;
 
-            while (node == null && control != null)
+            while (node == null && c != null)
             {
-                node = FindNode(control);
+                node = FindNode(c);
 
                 if (node == null)
                 {
-                    control = control.GetVisualParent<IControl>();
+                    c = c.GetVisualParent<IControl>();
                 }
             }
 
diff --git a/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj b/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj
index a1d249b8f7..475a3655e4 100644
--- a/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj
+++ b/src/Avalonia.Dialogs/Avalonia.Dialogs.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Avalonia.FreeDesktop/Avalonia.FreeDesktop.csproj b/src/Avalonia.FreeDesktop/Avalonia.FreeDesktop.csproj
index 897e7bf64d..bcb63783a4 100644
--- a/src/Avalonia.FreeDesktop/Avalonia.FreeDesktop.csproj
+++ b/src/Avalonia.FreeDesktop/Avalonia.FreeDesktop.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Avalonia.Headless.Vnc/Avalonia.Headless.Vnc.csproj b/src/Avalonia.Headless.Vnc/Avalonia.Headless.Vnc.csproj
index be91d5f056..273910eb59 100644
--- a/src/Avalonia.Headless.Vnc/Avalonia.Headless.Vnc.csproj
+++ b/src/Avalonia.Headless.Vnc/Avalonia.Headless.Vnc.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-      <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+      <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     </PropertyGroup>
 
     <ItemGroup>
diff --git a/src/Avalonia.Headless/Avalonia.Headless.csproj b/src/Avalonia.Headless/Avalonia.Headless.csproj
index 28666efdf2..2e33b5790a 100644
--- a/src/Avalonia.Headless/Avalonia.Headless.csproj
+++ b/src/Avalonia.Headless/Avalonia.Headless.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
 
   </PropertyGroup>
   <ItemGroup>
diff --git a/src/Avalonia.Input/AccessKeyHandler.cs b/src/Avalonia.Input/AccessKeyHandler.cs
index a3330b65ae..60175ae588 100644
--- a/src/Avalonia.Input/AccessKeyHandler.cs
+++ b/src/Avalonia.Input/AccessKeyHandler.cs
@@ -188,7 +188,7 @@ namespace Avalonia.Input
                 // If the menu is open, only match controls in the menu's visual tree.
                 if (menuIsOpen)
                 {
-                    matches = matches.Where(x => MainMenu.IsVisualAncestorOf(x));
+                    matches = matches.Where(x => x is not null && MainMenu!.IsVisualAncestorOf(x));
                 }
 
                 var match = matches.FirstOrDefault();
diff --git a/src/Avalonia.Input/Avalonia.Input.csproj b/src/Avalonia.Input/Avalonia.Input.csproj
index a1640a62f8..e66d1d7e7c 100644
--- a/src/Avalonia.Input/Avalonia.Input.csproj
+++ b/src/Avalonia.Input/Avalonia.Input.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="..\Avalonia.Base\Metadata\NullableAttributes.cs" Link="NullableAttributes.cs" />
diff --git a/src/Avalonia.Input/GestureRecognizers/ScrollGestureRecognizer.cs b/src/Avalonia.Input/GestureRecognizers/ScrollGestureRecognizer.cs
index 84a26a0cc3..f8cedb636f 100644
--- a/src/Avalonia.Input/GestureRecognizers/ScrollGestureRecognizer.cs
+++ b/src/Avalonia.Input/GestureRecognizers/ScrollGestureRecognizer.cs
@@ -71,7 +71,7 @@ namespace Avalonia.Input.GestureRecognizers
                 EndGesture();
                 _tracking = e.Pointer;
                 _gestureId = ScrollGestureEventArgs.GetNextFreeId();;
-                _trackedRootPoint = e.GetPosition(null);
+                _trackedRootPoint = e.GetPosition(_target);
             }
         }
 
@@ -85,7 +85,7 @@ namespace Avalonia.Input.GestureRecognizers
         {
             if (e.Pointer == _tracking)
             {
-                var rootPoint = e.GetPosition(null);
+                var rootPoint = e.GetPosition(_target);
                 if (!_scrolling)
                 {
                     if (CanHorizontallyScroll && Math.Abs(_trackedRootPoint.X - rootPoint.X) > ScrollStartDistance)
diff --git a/src/Avalonia.Input/Gestures.cs b/src/Avalonia.Input/Gestures.cs
index 639b4ef117..a5ee558f47 100644
--- a/src/Avalonia.Input/Gestures.cs
+++ b/src/Avalonia.Input/Gestures.cs
@@ -6,6 +6,7 @@ namespace Avalonia.Input
 {
     public static class Gestures
     {
+        private static bool s_isDoubleTapped = false;
         public static readonly RoutedEvent<TappedEventArgs> TappedEvent = RoutedEvent.Register<TappedEventArgs>(
             "Tapped",
             RoutingStrategies.Bubble,
@@ -81,20 +82,23 @@ namespace Avalonia.Input
                 var e = (PointerPressedEventArgs)ev;
                 var visual = (IVisual)ev.Source;
 
-#pragma warning disable CS0618 // Type or member is obsolete
-                var clickCount = e.ClickCount;
-#pragma warning restore CS0618 // Type or member is obsolete
-                if (clickCount <= 1)
+                if (e.ClickCount <= 1)
                 {
+                    s_isDoubleTapped = false;
                     s_lastPress.SetTarget(ev.Source);
                 }
-                else if (clickCount == 2 && e.GetCurrentPoint(visual).Properties.IsLeftButtonPressed)
+                else if (e.ClickCount % 2 == 0 && e.GetCurrentPoint(visual).Properties.IsLeftButtonPressed)
                 {
                     if (s_lastPress.TryGetTarget(out var target) && target == e.Source)
                     {
+                        s_isDoubleTapped = true;
                         e.Source.RaiseEvent(new TappedEventArgs(DoubleTappedEvent, e));
                     }
                 }
+                else
+                {
+                    s_isDoubleTapped = false;
+                }
             }
         }
 
@@ -112,7 +116,9 @@ namespace Avalonia.Input
                         {
                             e.Source.RaiseEvent(new TappedEventArgs(RightTappedEvent, e));
                         }
-                        else
+                        //s_isDoubleTapped needed here to prevent invoking Tapped event when DoubleTapped is called.
+                        //This behaviour matches UWP behaviour.
+                        else if (s_isDoubleTapped == false)
                         {
                             e.Source.RaiseEvent(new TappedEventArgs(TappedEvent, e));
                         }
diff --git a/src/Avalonia.Input/InputElement.cs b/src/Avalonia.Input/InputElement.cs
index c2197ee64d..def0a26b27 100644
--- a/src/Avalonia.Input/InputElement.cs
+++ b/src/Avalonia.Input/InputElement.cs
@@ -675,7 +675,7 @@ namespace Avalonia.Input
         /// <see cref="IsEffectivelyEnabled"/>.
         /// </summary>
         /// <param name="parent">The parent control.</param>
-        private void UpdateIsEffectivelyEnabled(InputElement parent)
+        private void UpdateIsEffectivelyEnabled(InputElement? parent)
         {
             IsEffectivelyEnabled = IsEnabledCore && (parent?.IsEffectivelyEnabled ?? true);
 
diff --git a/src/Avalonia.Input/Pointer.cs b/src/Avalonia.Input/Pointer.cs
index 433b275ce4..3012f07f6a 100644
--- a/src/Avalonia.Input/Pointer.cs
+++ b/src/Avalonia.Input/Pointer.cs
@@ -54,7 +54,7 @@ namespace Avalonia.Input
                 Captured.DetachedFromVisualTree += OnCaptureDetached;
         }
 
-        IInputElement GetNextCapture(IVisual parent)
+        IInputElement? GetNextCapture(IVisual parent)
         {
             return parent as IInputElement ?? parent.FindAncestorOfType<IInputElement>();
         }
diff --git a/src/Avalonia.Input/PointerEventArgs.cs b/src/Avalonia.Input/PointerEventArgs.cs
index ba39f7ca8e..8c86cd4637 100644
--- a/src/Avalonia.Input/PointerEventArgs.cs
+++ b/src/Avalonia.Input/PointerEventArgs.cs
@@ -114,7 +114,7 @@ namespace Avalonia.Input
 
     public class PointerPressedEventArgs : PointerEventArgs
     {
-        private readonly int _obsoleteClickCount;
+        private readonly int _clickCount;
 
         public PointerPressedEventArgs(
             IInteractive source,
@@ -123,15 +123,14 @@ namespace Avalonia.Input
             ulong timestamp,
             PointerPointProperties properties,
             KeyModifiers modifiers,
-            int obsoleteClickCount = 1)
+            int clickCount = 1)
             : base(InputElement.PointerPressedEvent, source, pointer, rootVisual, rootVisualPosition,
                 timestamp, properties, modifiers)
         {
-            _obsoleteClickCount = obsoleteClickCount;
+            _clickCount = clickCount;
         }
 
-        [Obsolete("Use DoubleTapped event or Gestures.DoubleRightTapped attached event")]
-        public int ClickCount => _obsoleteClickCount;
+        public int ClickCount => _clickCount;
 
         [Obsolete("Use PointerPressedEventArgs.GetCurrentPoint(this).Properties")]
         public MouseButton MouseButton => Properties.PointerUpdateKind.GetMouseButton();
diff --git a/src/Avalonia.Input/TouchDevice.cs b/src/Avalonia.Input/TouchDevice.cs
index d6ad836f37..af8851a82b 100644
--- a/src/Avalonia.Input/TouchDevice.cs
+++ b/src/Avalonia.Input/TouchDevice.cs
@@ -2,7 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using Avalonia.Input.Raw;
-using Avalonia.VisualTree;
+using Avalonia.Platform;
 
 namespace Avalonia.Input
 {
@@ -16,7 +16,9 @@ namespace Avalonia.Input
     {
         private readonly Dictionary<long, Pointer> _pointers = new Dictionary<long, Pointer>();
         private bool _disposed;
-        
+        private int _clickCount;
+        private Rect _lastClickRect;
+        private ulong _lastClickTime;
         KeyModifiers GetKeyModifiers(RawInputModifiers modifiers) =>
             (KeyModifiers)(modifiers & RawInputModifiers.KeyboardMask);
 
@@ -27,10 +29,10 @@ namespace Avalonia.Input
                 rv |= RawInputModifiers.LeftMouseButton;
             return rv;
         }
-        
+
         public void ProcessRawEvent(RawInputEventArgs ev)
         {
-            if(_disposed)
+            if (_disposed)
                 return;
             var args = (RawTouchEventArgs)ev;
             if (!_pointers.TryGetValue(args.TouchPointId, out var pointer))
@@ -43,16 +45,40 @@ namespace Avalonia.Input
                     PointerType.Touch, _pointers.Count == 0);
                 pointer.Capture(hit);
             }
-            
+
 
             var target = pointer.Captured ?? args.Root;
             if (args.Type == RawPointerEventType.TouchBegin)
             {
+                if (_pointers.Count > 1)
+                {
+                    _clickCount = 1;
+                    _lastClickTime = 0;
+                    _lastClickRect = new Rect();
+                }
+                else
+                {
+                    var settings = AvaloniaLocator.Current.GetService<IPlatformSettings>();
+                    if (settings == null)
+                    {
+                        throw new Exception("IPlatformSettings can not be null.");
+                    }
+                    if (!_lastClickRect.Contains(args.Position)
+                        || ev.Timestamp - _lastClickTime > settings.DoubleClickTime.TotalMilliseconds)
+                    {
+                        _clickCount = 0;
+                    }
+                    ++_clickCount;
+                    _lastClickTime = ev.Timestamp;
+                    _lastClickRect = new Rect(args.Position, new Size())
+                        .Inflate(new Thickness(16, 16));
+                }
+
                 target.RaiseEvent(new PointerPressedEventArgs(target, pointer,
                     args.Root, args.Position, ev.Timestamp,
                     new PointerPointProperties(GetModifiers(args.InputModifiers, true),
                         PointerUpdateKind.LeftButtonPressed),
-                    GetKeyModifiers(args.InputModifiers)));
+                    GetKeyModifiers(args.InputModifiers), _clickCount));
             }
 
             if (args.Type == RawPointerEventType.TouchEnd)
@@ -84,12 +110,12 @@ namespace Avalonia.Input
                     GetKeyModifiers(args.InputModifiers)));
             }
 
-            
+
         }
 
         public void Dispose()
         {
-            if(_disposed)
+            if (_disposed)
                 return;
             var values = _pointers.Values.ToList();
             _pointers.Clear();
@@ -97,6 +123,6 @@ namespace Avalonia.Input
             foreach (var p in values)
                 p.Dispose();
         }
-        
+
     }
 }
diff --git a/src/Avalonia.Interactivity/Avalonia.Interactivity.csproj b/src/Avalonia.Interactivity/Avalonia.Interactivity.csproj
index effb0e4c99..03a53f7d86 100644
--- a/src/Avalonia.Interactivity/Avalonia.Interactivity.csproj
+++ b/src/Avalonia.Interactivity/Avalonia.Interactivity.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Animation\Avalonia.Animation.csproj" />
diff --git a/src/Avalonia.Layout/AttachedLayout.cs b/src/Avalonia.Layout/AttachedLayout.cs
index 047c01343f..6c884641f8 100644
--- a/src/Avalonia.Layout/AttachedLayout.cs
+++ b/src/Avalonia.Layout/AttachedLayout.cs
@@ -12,17 +12,17 @@ namespace Avalonia.Layout
     /// </summary>
     public abstract class AttachedLayout : AvaloniaObject
     {
-        public string LayoutId { get; set; }
+        public string? LayoutId { get; set; }
 
         /// <summary>
         /// Occurs when the measurement state (layout) has been invalidated.
         /// </summary>
-        public event EventHandler MeasureInvalidated;
+        public event EventHandler? MeasureInvalidated;
 
         /// <summary>
         /// Occurs when the arrange state (layout) has been invalidated.
         /// </summary>
-        public event EventHandler ArrangeInvalidated;
+        public event EventHandler? ArrangeInvalidated;
 
         /// <summary>
         /// Initializes any per-container state the layout requires when it is attached to an
diff --git a/src/Avalonia.Layout/Avalonia.Layout.csproj b/src/Avalonia.Layout/Avalonia.Layout.csproj
index 2842ccf3a8..f2c4b0540b 100644
--- a/src/Avalonia.Layout/Avalonia.Layout.csproj
+++ b/src/Avalonia.Layout/Avalonia.Layout.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Avalonia.Animation\Avalonia.Animation.csproj" />
@@ -9,4 +9,5 @@
   </ItemGroup>  
   <Import Project="..\..\build\Rx.props" />
   <Import Project="..\..\build\ApiDiff.props" />
+  <Import Project="..\..\build\NullableEnable.props" />
 </Project>
diff --git a/src/Avalonia.Layout/ElementManager.cs b/src/Avalonia.Layout/ElementManager.cs
index 681d23a61f..9a033ca447 100644
--- a/src/Avalonia.Layout/ElementManager.cs
+++ b/src/Avalonia.Layout/ElementManager.cs
@@ -13,10 +13,10 @@ namespace Avalonia.Layout
 {
     internal class ElementManager
     {
-        private readonly List<ILayoutable> _realizedElements = new List<ILayoutable>();
+        private readonly List<ILayoutable?> _realizedElements = new List<ILayoutable?>();
         private readonly List<Rect> _realizedElementLayoutBounds = new List<Rect>();
         private int _firstRealizedDataIndex;
-        private VirtualizingLayoutContext _context;
+        private VirtualizingLayoutContext? _context;
 
         private bool IsVirtualizingContext
         {
@@ -58,7 +58,7 @@ namespace Avalonia.Layout
                         // Make sure there is enough space for the bounds.
                         // Note: We could optimize when the count becomes smaller, but keeping
                         // it always up to date is the simplest option for now.
-                        _realizedElementLayoutBounds.Resize(count);
+                        _realizedElementLayoutBounds.Resize(count, default);
                     }
                 }
             }
@@ -66,34 +66,32 @@ namespace Avalonia.Layout
 
         public int GetRealizedElementCount()
         {
-            return IsVirtualizingContext ? _realizedElements.Count : _context.ItemCount;
+            return IsVirtualizingContext ? _realizedElements.Count : _context!.ItemCount;
         }
 
         public ILayoutable GetAt(int realizedIndex)
         {
-            ILayoutable element;
+            ILayoutable? element;
 
             if (IsVirtualizingContext)
             {
-                if (_realizedElements[realizedIndex] == null)
+                element = _realizedElements[realizedIndex];
+
+                if (element == null)
                 {
                     // Sentinel. Create the element now since we need it.
                     int dataIndex = GetDataIndexFromRealizedRangeIndex(realizedIndex);
                     Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "Creating element for sentinal with data index {Index}", dataIndex);
-                    element = _context.GetOrCreateElementAt(
+                    element = _context!.GetOrCreateElementAt(
                         dataIndex,
                         ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
                     _realizedElements[realizedIndex] = element;
                 }
-                else
-                {
-                    element = _realizedElements[realizedIndex];
-                }
             }
             else
             {
                 // realizedIndex and dataIndex are the same (everything is realized)
-                element = _context.GetOrCreateElementAt(
+                element = _context!.GetOrCreateElementAt(
                     realizedIndex,
                     ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
             }
@@ -112,7 +110,7 @@ namespace Avalonia.Layout
             _realizedElementLayoutBounds.Add(default);
         }
 
-        public void Insert(int realizedIndex, int dataIndex, ILayoutable element)
+        public void Insert(int realizedIndex, int dataIndex, ILayoutable? element)
         {
             if (realizedIndex == 0)
             {
@@ -136,7 +134,7 @@ namespace Avalonia.Layout
 
                 if (elementRef != null)
                 {
-                    _context.RecycleElement(elementRef);
+                    _context!.RecycleElement(elementRef);
                 }
             }
 
@@ -203,26 +201,26 @@ namespace Avalonia.Layout
             else
             {
                 // Non virtualized - everything is realized
-                return index >= 0 && index < _context.ItemCount;
+                return index >= 0 && index < _context!.ItemCount;
             }
         }
 
-        public bool IsIndexValidInData(int currentIndex) => (uint)currentIndex < _context.ItemCount;
+        public bool IsIndexValidInData(int currentIndex) => (uint)currentIndex < _context!.ItemCount;
 
-        public ILayoutable GetRealizedElement(int dataIndex)
+        public ILayoutable? GetRealizedElement(int dataIndex)
         {
             return IsVirtualizingContext ?
                 GetAt(GetRealizedRangeIndexFromDataIndex(dataIndex)) :
-                _context.GetOrCreateElementAt(
+                _context!.GetOrCreateElementAt(
                     dataIndex,
                     ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
         }
 
-        public void EnsureElementRealized(bool forward, int dataIndex, string layoutId)
+        public void EnsureElementRealized(bool forward, int dataIndex, string? layoutId)
         {
             if (IsDataIndexRealized(dataIndex) == false)
             {
-                var element = _context.GetOrCreateElementAt(
+                var element = _context!.GetOrCreateElementAt(
                     dataIndex,
                     ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
 
@@ -273,14 +271,14 @@ namespace Avalonia.Layout
                 {
                     case NotifyCollectionChangedAction.Add:
                         {
-                            OnItemsAdded(args.NewStartingIndex, args.NewItems.Count);
+                            OnItemsAdded(args.NewStartingIndex, args.NewItems!.Count);
                         }
                         break;
 
                     case NotifyCollectionChangedAction.Replace:
                         {
-                            int oldSize = args.OldItems.Count;
-                            int newSize = args.NewItems.Count;
+                            int oldSize = args.OldItems!.Count;
+                            int newSize = args.NewItems!.Count;
                             int oldStartIndex = args.OldStartingIndex;
                             int newStartIndex = args.NewStartingIndex;
 
@@ -301,7 +299,7 @@ namespace Avalonia.Layout
 
                                     if (elementRef != null)
                                     {
-                                        _context.RecycleElement(elementRef);
+                                        _context!.RecycleElement(elementRef);
                                         _realizedElements[realizedIndex] = null;
                                     }
                                 }
diff --git a/src/Avalonia.Layout/FlowLayoutAlgorithm.cs b/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
index 63343fd1a7..40b392225f 100644
--- a/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
+++ b/src/Avalonia.Layout/FlowLayoutAlgorithm.cs
@@ -16,8 +16,8 @@ namespace Avalonia.Layout
         private Size _lastAvailableSize;
         private double _lastItemSpacing;
         private bool _collectionChangePending;
-        private VirtualizingLayoutContext _context;
-        private IFlowLayoutAlgorithmDelegates _algorithmCallbacks;
+        private VirtualizingLayoutContext? _context;
+        private IFlowLayoutAlgorithmDelegates? _algorithmCallbacks;
         private Rect _lastExtent;
         private int _firstRealizedDataIndexInsideRealizationWindow = -1;
         private int _lastRealizedDataIndexInsideRealizationWindow = -1;
@@ -46,7 +46,7 @@ namespace Avalonia.Layout
             }
         }
 
-        private Rect RealizationRect => IsVirtualizingContext ? _context.RealizationRect : new Rect(Size.Infinity);
+        private Rect RealizationRect => IsVirtualizingContext ? _context!.RealizationRect : new Rect(Size.Infinity);
 
         public void InitializeForContext(VirtualizingLayoutContext context, IFlowLayoutAlgorithmDelegates callbacks)
         {
@@ -76,7 +76,7 @@ namespace Avalonia.Layout
             int maxItemsPerLine,
             ScrollOrientation orientation,
             bool disableVirtualization,
-            string layoutId)
+            string? layoutId)
         {
             _orientation.ScrollOrientation = orientation;
 
@@ -87,7 +87,7 @@ namespace Avalonia.Layout
                 layoutId,
                 realizationRect);
 
-            var suggestedAnchorIndex = _context.RecommendedAnchorIndex;
+            var suggestedAnchorIndex = _context!.RecommendedAnchorIndex;
             if (_elementManager.IsIndexValidInData(suggestedAnchorIndex))
             {
                 var anchorRealized = _elementManager.IsDataIndexRealized(suggestedAnchorIndex);
@@ -124,7 +124,7 @@ namespace Avalonia.Layout
             VirtualizingLayoutContext context,
             bool isWrapping,
             LineAlignment lineAlignment,
-            string layoutId)
+            string? layoutId)
         {
             Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: ArrangeLayout", layoutId);
             ArrangeVirtualizingLayout(finalSize, lineAlignment, isWrapping, layoutId);
@@ -149,7 +149,7 @@ namespace Avalonia.Layout
             Size availableSize,
             VirtualizingLayoutContext context)
         {
-            var measureSize = _algorithmCallbacks.Algorithm_GetMeasureSize(index, availableSize, context);
+            var measureSize = _algorithmCallbacks!.Algorithm_GetMeasureSize(index, availableSize, context);
             element.Measure(measureSize);
             var provisionalArrangeSize = _algorithmCallbacks.Algorithm_GetProvisionalArrangeSize(index, measureSize, element.DesiredSize, context);
             _algorithmCallbacks.Algorithm_OnElementMeasured(element, index, availableSize, measureSize, element.DesiredSize, provisionalArrangeSize, context);
@@ -161,7 +161,7 @@ namespace Avalonia.Layout
             Size availableSize,
             bool isWrapping,
             double minItemSpacing,
-            string layoutId)
+            string? layoutId)
         {
             int anchorIndex = -1;
             var anchorPosition= new Point();
@@ -170,7 +170,7 @@ namespace Avalonia.Layout
             if (!IsVirtualizingContext)
             {
                 // Non virtualizing host, start generating from the element 0
-                anchorIndex = context.ItemCount > 0 ? 0 : -1;
+                anchorIndex = context!.ItemCount > 0 ? 0 : -1;
             }
             else
             {       
@@ -183,7 +183,7 @@ namespace Avalonia.Layout
                     _lastItemSpacing != minItemSpacing ||
                     _collectionChangePending);
 
-                var suggestedAnchorIndex = _context.RecommendedAnchorIndex;
+                var suggestedAnchorIndex = _context!.RecommendedAnchorIndex;
 
                 var isAnchorSuggestionValid = suggestedAnchorIndex >= 0 &&
                     _elementManager.IsDataIndexRealized(suggestedAnchorIndex);
@@ -191,10 +191,10 @@ namespace Avalonia.Layout
                 if (isAnchorSuggestionValid)
                 {
                     Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId}: Using suggested anchor {Anchor}", layoutId, suggestedAnchorIndex);
-                    anchorIndex = _algorithmCallbacks.Algorithm_GetAnchorForTargetElement(
+                    anchorIndex = _algorithmCallbacks!.Algorithm_GetAnchorForTargetElement(
                         suggestedAnchorIndex,
                         availableSize,
-                        context).Index;
+                        context!).Index;
 
                     if (_elementManager.IsDataIndexRealized(anchorIndex))
                     {
@@ -235,7 +235,7 @@ namespace Avalonia.Layout
 
                     // The anchor is based on the realization window because a connected ItemsRepeater might intersect the realization window
                     // but not the visible window. In that situation, we still need to produce a valid anchor.
-                    var anchorInfo = _algorithmCallbacks.Algorithm_GetAnchorForRealizationRect(availableSize, context);
+                    var anchorInfo = _algorithmCallbacks!.Algorithm_GetAnchorForRealizationRect(availableSize, context!);
                     anchorIndex = anchorInfo.Index;
                     anchorPosition = _orientation.MinorMajorPoint(0, anchorInfo.Offset);
                 }
@@ -259,12 +259,12 @@ namespace Avalonia.Layout
                     Logger.TryGet(LogEventLevel.Verbose, "Repeater")?.Log(this, "{LayoutId} Disconnected Window - throwing away all realized elements", layoutId);
                     _elementManager.ClearRealizedRange();
 
-                    var anchor = _context.GetOrCreateElementAt(anchorIndex, ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
+                    var anchor = _context!.GetOrCreateElementAt(anchorIndex, ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
                     _elementManager.Add(anchor, anchorIndex);
                 }
 
                 var anchorElement = _elementManager.GetRealizedElement(anchorIndex);
-                var desiredSize = MeasureElement(anchorElement, anchorIndex, availableSize, _context);
+                var desiredSize = MeasureElement(anchorElement!, anchorIndex, availableSize, _context!);
                 var layoutBounds = new Rect(anchorPosition.X, anchorPosition.Y, desiredSize.Width, desiredSize.Height);
                 _elementManager.SetLayoutBoundsForDataIndex(anchorIndex, layoutBounds);
 
@@ -296,7 +296,7 @@ namespace Avalonia.Layout
             double lineSpacing,
             int maxItemsPerLine,
             bool disableVirtualization,
-            string layoutId)
+            string? layoutId)
         {
             if (anchorIndex != -1)
             {
@@ -322,7 +322,7 @@ namespace Avalonia.Layout
                     // Ensure layout element.
                     _elementManager.EnsureElementRealized(direction == GenerateDirection.Forward, currentIndex, layoutId);
                     var currentElement = _elementManager.GetRealizedElement(currentIndex);
-                    var desiredSize = MeasureElement(currentElement, currentIndex, availableSize, _context);
+                    var desiredSize = MeasureElement(currentElement!, currentIndex, availableSize, _context!);
                     ++count;
 
                     // Lay it out.
@@ -333,7 +333,7 @@ namespace Avalonia.Layout
                     if (direction == GenerateDirection.Forward)
                     {
                         double remainingSpace = _orientation.Minor(availableSize) - (_orientation.MinorStart(previousElementBounds) + _orientation.MinorSize(previousElementBounds) + minItemSpacing + _orientation.Minor(desiredSize));
-                        if (countInLine >= maxItemsPerLine || _algorithmCallbacks.Algorithm_ShouldBreakLine(currentIndex, remainingSpace))
+                        if (countInLine >= maxItemsPerLine || _algorithmCallbacks!.Algorithm_ShouldBreakLine(currentIndex, remainingSpace))
                         {
                             // No more space in this row. wrap to next row.
                             _orientation.SetMinorStart(ref currentBounds, 0);
@@ -371,7 +371,7 @@ namespace Avalonia.Layout
                     {
                         // Backward 
                         double remainingSpace = _orientation.MinorStart(previousElementBounds) - (_orientation.Minor(desiredSize) + minItemSpacing);
-                        if (countInLine >= maxItemsPerLine || _algorithmCallbacks.Algorithm_ShouldBreakLine(currentIndex, remainingSpace))
+                        if (countInLine >= maxItemsPerLine || _algorithmCallbacks!.Algorithm_ShouldBreakLine(currentIndex, remainingSpace))
                         {
                             // Does not fit, wrap to the previous row
                             var availableSizeMinor = _orientation.Minor(availableSize);
@@ -432,13 +432,13 @@ namespace Avalonia.Layout
                 // account for that element in the indices inside the realization window.
                 if (direction == GenerateDirection.Forward)
                 {
-                    int dataCount = _context.ItemCount;
+                    int dataCount = _context!.ItemCount;
                     _lastRealizedDataIndexInsideRealizationWindow = previousIndex == dataCount - 1 ? dataCount - 1 : previousIndex - 1;
                     _lastRealizedDataIndexInsideRealizationWindow = Math.Max(0, _lastRealizedDataIndexInsideRealizationWindow);
                 }
                 else
                 {
-                    int dataCount = _context.ItemCount;
+                    int dataCount = _context!.ItemCount;
                     _firstRealizedDataIndexInsideRealizationWindow = previousIndex == 0 ? 0 : previousIndex + 1;
                     _firstRealizedDataIndexInsideRealizationWindow = Math.Min(dataCount - 1, _firstRealizedDataIndexInsideRealizationWindow);
                 }
@@ -454,7 +454,7 @@ namespace Avalonia.Layout
         {
             _elementManager.ClearRealizedRange();
             // FlowLayout requires that the anchor is the first element in the row.
-            var internalAnchor = _algorithmCallbacks.Algorithm_GetAnchorForTargetElement(index, availableSize, context);
+            var internalAnchor = _algorithmCallbacks!.Algorithm_GetAnchorForTargetElement(index, availableSize, context);
 
             // No need to set the position of the anchor.
             // (0,0) is fine for now since the extent can
@@ -487,7 +487,7 @@ namespace Avalonia.Layout
             }
             else
             {
-                var realizationRect = _context.RealizationRect;
+                var realizationRect = _context!.RealizationRect;
                 var elementBounds = _elementManager.GetLayoutBoundsForDataIndex(index);
 
                 var elementMajorStart = _orientation.MajorStart(elementBounds);
@@ -510,11 +510,11 @@ namespace Avalonia.Layout
             return shouldContinue;
         }
 
-        private Rect EstimateExtent(Size availableSize, string layoutId)
+        private Rect EstimateExtent(Size availableSize, string? layoutId)
         {
-            ILayoutable firstRealizedElement = null;
+            ILayoutable? firstRealizedElement = null;
             Rect firstBounds = new Rect();
-            ILayoutable lastRealizedElement = null;
+            ILayoutable? lastRealizedElement = null;
             Rect lastBounds = new Rect();
             int firstDataIndex = -1;
             int lastDataIndex = -1;
@@ -531,9 +531,9 @@ namespace Avalonia.Layout
                 lastBounds = _elementManager.GetLayoutBoundsForRealizedIndex(last);
             }
 
-            Rect extent = _algorithmCallbacks.Algorithm_GetExtent(
+            Rect extent = _algorithmCallbacks!.Algorithm_GetExtent(
                 availableSize,
-                _context,
+                _context!,
                 firstRealizedElement,
                 firstDataIndex,
                 firstBounds,
@@ -563,7 +563,7 @@ namespace Avalonia.Layout
                         if (_orientation.MajorStart(currentBounds) != currentLineOffset)
                         {
                             // Staring a new line
-                            _algorithmCallbacks.Algorithm_OnLineArranged(currentDataIndex - countInLine, countInLine, currentLineSize, _context);
+                            _algorithmCallbacks!.Algorithm_OnLineArranged(currentDataIndex - countInLine, countInLine, currentLineSize, _context!);
                             countInLine = 0;
                             currentLineOffset = _orientation.MajorStart(currentBounds);
                             currentLineSize = 0;
@@ -575,7 +575,7 @@ namespace Avalonia.Layout
                     }
 
                     // Raise for the last line.
-                    _algorithmCallbacks.Algorithm_OnLineArranged(_lastRealizedDataIndexInsideRealizationWindow - countInLine + 1, countInLine, currentLineSize, _context);
+                    _algorithmCallbacks!.Algorithm_OnLineArranged(_lastRealizedDataIndexInsideRealizationWindow - countInLine + 1, countInLine, currentLineSize, _context!);
                 }
             }
         }
@@ -584,7 +584,7 @@ namespace Avalonia.Layout
             Size finalSize,
             LineAlignment lineAlignment,
             bool isWrapping,
-            string layoutId)
+            string? layoutId)
         {
             // Walk through the realized elements one line at a time and 
             // align them, Then call element.Arrange with the arranged bounds.
@@ -636,7 +636,7 @@ namespace Avalonia.Layout
             LineAlignment lineAlignment,
             bool isWrapping,
             Size finalSize,
-            string layoutId)
+            string? layoutId)
         {
             for (int rangeIndex = lineStartIndex; rangeIndex < lineStartIndex + countInLine; ++rangeIndex)
             {
@@ -723,11 +723,11 @@ namespace Avalonia.Layout
         {
             if (IsVirtualizingContext)
             {
-                _context.LayoutOrigin = new Point(_lastExtent.X, _lastExtent.Y);
+                _context!.LayoutOrigin = new Point(_lastExtent.X, _lastExtent.Y);
             }
         }
 
-        public ILayoutable GetElementIfRealized(int dataIndex)
+        public ILayoutable? GetElementIfRealized(int dataIndex)
         {
             if (_elementManager.IsDataIndexRealized(dataIndex))
             {
diff --git a/src/Avalonia.Layout/IFlowLayoutAlgorithmDelegates.cs b/src/Avalonia.Layout/IFlowLayoutAlgorithmDelegates.cs
index 907a3adf0f..e3eae0caf7 100644
--- a/src/Avalonia.Layout/IFlowLayoutAlgorithmDelegates.cs
+++ b/src/Avalonia.Layout/IFlowLayoutAlgorithmDelegates.cs
@@ -21,10 +21,10 @@ namespace Avalonia.Layout
         Rect Algorithm_GetExtent(
             Size availableSize,
             VirtualizingLayoutContext context,
-            ILayoutable firstRealized,
+            ILayoutable? firstRealized,
             int firstRealizedItemIndex,
             Rect firstRealizedLayoutBounds,
-            ILayoutable lastRealized,
+            ILayoutable? lastRealized,
             int lastRealizedItemIndex,
             Rect lastRealizedLayoutBounds);
         void Algorithm_OnElementMeasured(
diff --git a/src/Avalonia.Layout/LayoutContext.cs b/src/Avalonia.Layout/LayoutContext.cs
index dadce58c0c..90bfc0200c 100644
--- a/src/Avalonia.Layout/LayoutContext.cs
+++ b/src/Avalonia.Layout/LayoutContext.cs
@@ -14,7 +14,7 @@ namespace Avalonia.Layout
         /// <summary>
         /// Gets or sets an object that represents the state of a layout.
         /// </summary>
-        public object LayoutState 
+        public object? LayoutState 
         {
             get => LayoutStateCore;
             set => LayoutStateCore = value;
@@ -23,6 +23,6 @@ namespace Avalonia.Layout
         /// <summary>
         /// Implements the behavior of <see cref="LayoutState"/> in a derived or custom LayoutContext.
         /// </summary>
-        protected virtual object LayoutStateCore { get; set; }
+        protected virtual object? LayoutStateCore { get; set; }
     }
 }
diff --git a/src/Avalonia.Layout/LayoutContextAdapter.cs b/src/Avalonia.Layout/LayoutContextAdapter.cs
index 695866df94..25132c2802 100644
--- a/src/Avalonia.Layout/LayoutContextAdapter.cs
+++ b/src/Avalonia.Layout/LayoutContextAdapter.cs
@@ -16,7 +16,7 @@ namespace Avalonia.Layout
             _nonVirtualizingContext = nonVirtualizingContext;
         }
 
-        protected override object LayoutStateCore 
+        protected override object? LayoutStateCore 
         { 
             get => _nonVirtualizingContext.LayoutState;
             set => _nonVirtualizingContext.LayoutState = value; 
diff --git a/src/Avalonia.Layout/LayoutHelper.cs b/src/Avalonia.Layout/LayoutHelper.cs
index 2fe59b49ca..71a2fa085b 100644
--- a/src/Avalonia.Layout/LayoutHelper.cs
+++ b/src/Avalonia.Layout/LayoutHelper.cs
@@ -101,7 +101,7 @@ namespace Avalonia.Layout
 
             if (result == 0 || double.IsNaN(result) || double.IsInfinity(result))
             {
-                throw new Exception($"Invalid LayoutScaling returned from {visualRoot.GetType()}");
+                throw new Exception($"Invalid LayoutScaling returned from {visualRoot!.GetType()}");
             }
 
             return result;
diff --git a/src/Avalonia.Layout/LayoutQueue.cs b/src/Avalonia.Layout/LayoutQueue.cs
index 1a9eb6b785..24adeb0793 100644
--- a/src/Avalonia.Layout/LayoutQueue.cs
+++ b/src/Avalonia.Layout/LayoutQueue.cs
@@ -5,6 +5,7 @@ using System.Collections.Generic;
 namespace Avalonia.Layout
 {
     internal class LayoutQueue<T> : IReadOnlyCollection<T>, IDisposable
+        where T : notnull
     {
         private struct Info
         {
diff --git a/src/Avalonia.Layout/Layoutable.cs b/src/Avalonia.Layout/Layoutable.cs
index 7568ea8e09..09e0c4263a 100644
--- a/src/Avalonia.Layout/Layoutable.cs
+++ b/src/Avalonia.Layout/Layoutable.cs
@@ -794,7 +794,7 @@ namespace Avalonia.Layout
         /// </summary>
         /// <param name="sender">The sender.</param>
         /// <param name="e">The event args.</param>
-        private void LayoutManagedLayoutUpdated(object sender, EventArgs e) => _layoutUpdated?.Invoke(this, e);
+        private void LayoutManagedLayoutUpdated(object? sender, EventArgs e) => _layoutUpdated?.Invoke(this, e);
 
         /// <summary>
         /// Tests whether any of a <see cref="Rect"/>'s properties include negative values,
diff --git a/src/Avalonia.Layout/NonVirtualizingLayoutContext.cs b/src/Avalonia.Layout/NonVirtualizingLayoutContext.cs
index cef551f32e..91348f5e6d 100644
--- a/src/Avalonia.Layout/NonVirtualizingLayoutContext.cs
+++ b/src/Avalonia.Layout/NonVirtualizingLayoutContext.cs
@@ -12,7 +12,7 @@ namespace Avalonia.Layout
     /// </summary>
     public abstract class NonVirtualizingLayoutContext : LayoutContext
     {
-        private VirtualizingLayoutContext _contextAdapter;
+        private VirtualizingLayoutContext? _contextAdapter;
 
         /// <summary>
         /// Gets the collection of child controls from the container that provides the context.
@@ -26,6 +26,6 @@ namespace Avalonia.Layout
         protected abstract IReadOnlyList<ILayoutable> ChildrenCore { get; }
 
         internal VirtualizingLayoutContext GetVirtualizingContextAdapter() =>
-            _contextAdapter ?? (_contextAdapter = new LayoutContextAdapter(this));
+            _contextAdapter ??= new LayoutContextAdapter(this);
     }
 }
diff --git a/src/Avalonia.Layout/StackLayout.cs b/src/Avalonia.Layout/StackLayout.cs
index 4a93c8344f..32e9c4dc8e 100644
--- a/src/Avalonia.Layout/StackLayout.cs
+++ b/src/Avalonia.Layout/StackLayout.cs
@@ -78,10 +78,10 @@ namespace Avalonia.Layout
         internal Rect GetExtent(
             Size availableSize,
             VirtualizingLayoutContext context,
-            ILayoutable firstRealized,
+            ILayoutable? firstRealized,
             int firstRealizedItemIndex,
             Rect firstRealizedLayoutBounds,
-            ILayoutable lastRealized,
+            ILayoutable? lastRealized,
             int lastRealizedItemIndex,
             Rect lastRealizedLayoutBounds)
         {
@@ -89,7 +89,7 @@ namespace Avalonia.Layout
 
             // Constants
             int itemsCount = context.ItemCount;
-            var stackState = (StackLayoutState)context.LayoutState;
+            var stackState = (StackLayoutState)context.LayoutState!;
             double averageElementSize = GetAverageElementSize(availableSize, context, stackState) + Spacing;
 
             _orientation.SetMinorSize(ref extent, stackState.MaxArrangeBounds);
@@ -131,7 +131,7 @@ namespace Avalonia.Layout
         {
             if (context is VirtualizingLayoutContext virtualContext)
             {
-                var stackState = (StackLayoutState)virtualContext.LayoutState;
+                var stackState = (StackLayoutState)virtualContext.LayoutState!;
                 var provisionalArrangeSizeWinRt = provisionalArrangeSize;
                 stackState.OnElementMeasured(
                     index,
@@ -177,7 +177,7 @@ namespace Avalonia.Layout
             if (targetIndex >= 0 && targetIndex < itemsCount)
             {
                 index = targetIndex;
-                var state = (StackLayoutState)context.LayoutState;
+                var state = (StackLayoutState)context.LayoutState!;
                 double averageElementSize = GetAverageElementSize(availableSize, context, state) + Spacing;
                 offset = index * averageElementSize + _orientation.MajorStart(state.FlowAlgorithm.LastExtent);
             }
@@ -188,10 +188,10 @@ namespace Avalonia.Layout
         Rect IFlowLayoutAlgorithmDelegates.Algorithm_GetExtent(
             Size availableSize,
             VirtualizingLayoutContext context,
-            ILayoutable firstRealized,
+            ILayoutable? firstRealized,
             int firstRealizedItemIndex,
             Rect firstRealizedLayoutBounds,
-            ILayoutable lastRealized,
+            ILayoutable? lastRealized,
             int lastRealizedItemIndex,
             Rect lastRealizedLayoutBounds)
         {
@@ -234,7 +234,7 @@ namespace Avalonia.Layout
             if (itemsCount > 0)
             {
                 var realizationRect = context.RealizationRect;
-                var state = (StackLayoutState)context.LayoutState;
+                var state = (StackLayoutState)context.LayoutState!;
                 var lastExtent = state.FlowAlgorithm.LastExtent;
 
                 double averageElementSize = GetAverageElementSize(availableSize, context, state) + Spacing;
@@ -279,13 +279,13 @@ namespace Avalonia.Layout
 
         protected internal override void UninitializeForContextCore(VirtualizingLayoutContext context)
         {
-            var stackState = (StackLayoutState)context.LayoutState;
+            var stackState = (StackLayoutState)context.LayoutState!;
             stackState.UninitializeForContext(context);
         }
 
         protected internal override Size MeasureOverride(VirtualizingLayoutContext context, Size availableSize)
         {
-            ((StackLayoutState)context.LayoutState).OnMeasureStart();
+            ((StackLayoutState)context.LayoutState!).OnMeasureStart();
 
             var desiredSize = GetFlowAlgorithm(context).Measure(
                 availableSize,
@@ -358,6 +358,6 @@ namespace Avalonia.Layout
 
         private void InvalidateLayout() => InvalidateMeasure();
 
-        private FlowLayoutAlgorithm GetFlowAlgorithm(VirtualizingLayoutContext context) => ((StackLayoutState)context.LayoutState).FlowAlgorithm;
+        private FlowLayoutAlgorithm GetFlowAlgorithm(VirtualizingLayoutContext context) => ((StackLayoutState)context.LayoutState!).FlowAlgorithm;
     }
 }
diff --git a/src/Avalonia.Layout/UniformGridLayout.cs b/src/Avalonia.Layout/UniformGridLayout.cs
index 6b147590ab..508113834a 100644
--- a/src/Avalonia.Layout/UniformGridLayout.cs
+++ b/src/Avalonia.Layout/UniformGridLayout.cs
@@ -258,7 +258,7 @@ namespace Avalonia.Layout
             Size availableSize,
             VirtualizingLayoutContext context)
         {
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             return new Size(gridState.EffectiveItemWidth, gridState.EffectiveItemHeight);
         }
 
@@ -268,7 +268,7 @@ namespace Avalonia.Layout
             Size desiredSize,
             VirtualizingLayoutContext context)
         {
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             return new Size(gridState.EffectiveItemWidth, gridState.EffectiveItemHeight);
         }
 
@@ -285,7 +285,7 @@ namespace Avalonia.Layout
             var realizationRect = context.RealizationRect;
             if (itemsCount > 0 && _orientation.MajorSize(realizationRect) > 0)
             {
-                var gridState = (UniformGridLayoutState)context.LayoutState;
+                var gridState = (UniformGridLayoutState)context.LayoutState!;
                 var lastExtent = gridState.FlowAlgorithm.LastExtent;
                 var itemsPerLine = Math.Min( // note use of unsigned ints
                     Math.Max(1u, (uint)(_orientation.Minor(availableSize) / GetMinorSizeWithSpacing(context))),
@@ -324,7 +324,7 @@ namespace Avalonia.Layout
                     Math.Max(1u, _maximumRowsOrColumns));
                 int indexOfFirstInLine = (targetIndex / itemsPerLine) * itemsPerLine;
                 index = indexOfFirstInLine;
-                var state = context.LayoutState as UniformGridLayoutState;
+                var state = (UniformGridLayoutState)context.LayoutState!;
                 offset = _orientation.MajorStart(GetLayoutRectForDataIndex(availableSize, indexOfFirstInLine, state.FlowAlgorithm.LastExtent, context));
             }
 
@@ -338,10 +338,10 @@ namespace Avalonia.Layout
         Rect IFlowLayoutAlgorithmDelegates.Algorithm_GetExtent(
             Size availableSize,
             VirtualizingLayoutContext context,
-            ILayoutable firstRealized,
+            ILayoutable? firstRealized,
             int firstRealizedItemIndex,
             Rect firstRealizedLayoutBounds,
-            ILayoutable lastRealized,
+            ILayoutable? lastRealized,
             int lastRealizedItemIndex,
             Rect lastRealizedLayoutBounds)
         {
@@ -421,7 +421,7 @@ namespace Avalonia.Layout
 
         protected internal override void UninitializeForContextCore(VirtualizingLayoutContext context)
         {
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             gridState.UninitializeForContext(context);
         }
 
@@ -429,7 +429,7 @@ namespace Avalonia.Layout
         {
             // Set the width and height on the grid state. If the user already set them then use the preset. 
             // If not, we have to measure the first element and get back a size which we're going to be using for the rest of the items.
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             gridState.EnsureElementSize(availableSize, context, _minItemWidth, _minItemHeight, _itemsStretch, Orientation, MinRowSpacing, MinColumnSpacing, _maximumRowsOrColumns);
 
             var desiredSize = GetFlowAlgorithm(context).Measure(
@@ -467,7 +467,7 @@ namespace Avalonia.Layout
             // Always invalidate layout to keep the view accurate.
             InvalidateLayout();
 
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             gridState.ClearElementOnDataSourceChange(context, args);
         }
 
@@ -517,7 +517,7 @@ namespace Avalonia.Layout
         private double GetMinorSizeWithSpacing(VirtualizingLayoutContext context)
         {
             var minItemSpacing = MinItemSpacing;
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             return _orientation.ScrollOrientation == ScrollOrientation.Vertical?
                 gridState.EffectiveItemWidth + minItemSpacing :
                 gridState.EffectiveItemHeight + minItemSpacing;
@@ -526,7 +526,7 @@ namespace Avalonia.Layout
         private double GetMajorSizeWithSpacing(VirtualizingLayoutContext context)
         {
             var lineSpacing = LineSpacing;
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             return _orientation.ScrollOrientation == ScrollOrientation.Vertical ?
                 gridState.EffectiveItemHeight + lineSpacing :
                 gridState.EffectiveItemWidth + lineSpacing;
@@ -544,7 +544,7 @@ namespace Avalonia.Layout
             int rowIndex = (int)(index / itemsPerLine);
             int indexInRow = index - (rowIndex * itemsPerLine);
 
-            var gridState = (UniformGridLayoutState)context.LayoutState;
+            var gridState = (UniformGridLayoutState)context.LayoutState!;
             Rect bounds = _orientation.MinorMajorRect(
                 indexInRow * GetMinorSizeWithSpacing(context) + _orientation.MinorStart(lastExtent),
                 rowIndex * GetMajorSizeWithSpacing(context) + _orientation.MajorStart(lastExtent),
@@ -556,6 +556,6 @@ namespace Avalonia.Layout
 
         private void InvalidateLayout() => InvalidateMeasure();
 
-        private FlowLayoutAlgorithm GetFlowAlgorithm(VirtualizingLayoutContext context) => ((UniformGridLayoutState)context.LayoutState).FlowAlgorithm;
+        private FlowLayoutAlgorithm GetFlowAlgorithm(VirtualizingLayoutContext context) => ((UniformGridLayoutState)context.LayoutState!).FlowAlgorithm;
     }
 }
diff --git a/src/Avalonia.Layout/UniformGridLayoutState.cs b/src/Avalonia.Layout/UniformGridLayoutState.cs
index 282bbab1a8..d6b5a30bfc 100644
--- a/src/Avalonia.Layout/UniformGridLayoutState.cs
+++ b/src/Avalonia.Layout/UniformGridLayoutState.cs
@@ -18,7 +18,7 @@ namespace Avalonia.Layout
         // If it does not, then we need to do context.GetElement(0) at which point we have requested an element and are on point to clear it.
         // If we are responsible for clearing element 0 we keep m_cachedFirstElement valid. 
         // If we are not (because FlowLayoutAlgorithm is holding it for us) then we just null out this field and use the one from FlowLayoutAlgorithm.
-        private ILayoutable _cachedFirstElement;
+        private ILayoutable? _cachedFirstElement;
 
         internal FlowLayoutAlgorithm FlowAlgorithm { get; } = new FlowLayoutAlgorithm();
         internal double EffectiveItemWidth { get; private set; }
diff --git a/src/Avalonia.Layout/Utils/ListUtils.cs b/src/Avalonia.Layout/Utils/ListUtils.cs
index eb2480acd3..9ca8bb0525 100644
--- a/src/Avalonia.Layout/Utils/ListUtils.cs
+++ b/src/Avalonia.Layout/Utils/ListUtils.cs
@@ -23,10 +23,5 @@ namespace Avalonia.Layout.Utils
                 list.AddRange(Enumerable.Repeat(value, size - cur));
             }
         }
-
-        public static void Resize<T>(this List<T> list, int count)
-        {
-            Resize(list, count, default);
-        }
     }
 }
diff --git a/src/Avalonia.Layout/VirtualLayoutContextAdapter.cs b/src/Avalonia.Layout/VirtualLayoutContextAdapter.cs
index 80ccee2114..f068187523 100644
--- a/src/Avalonia.Layout/VirtualLayoutContextAdapter.cs
+++ b/src/Avalonia.Layout/VirtualLayoutContextAdapter.cs
@@ -6,14 +6,14 @@ namespace Avalonia.Layout
     public class VirtualLayoutContextAdapter : NonVirtualizingLayoutContext
     {
         private readonly VirtualizingLayoutContext _virtualizingContext;
-        private ChildrenCollection _children;
+        private ChildrenCollection? _children;
 
         public VirtualLayoutContextAdapter(VirtualizingLayoutContext virtualizingContext)
         {
             _virtualizingContext = virtualizingContext;
         }
 
-        protected override object LayoutStateCore
+        protected override object? LayoutStateCore
         {
             get => _virtualizingContext.LayoutState;
             set => _virtualizingContext.LayoutState = value;
diff --git a/src/Avalonia.Layout/VirtualizingLayoutContext.cs b/src/Avalonia.Layout/VirtualizingLayoutContext.cs
index 079b91a90f..f48c9b0ef2 100644
--- a/src/Avalonia.Layout/VirtualizingLayoutContext.cs
+++ b/src/Avalonia.Layout/VirtualizingLayoutContext.cs
@@ -43,7 +43,7 @@ namespace Avalonia.Layout
     /// </summary>
     public abstract class VirtualizingLayoutContext : LayoutContext
     {
-        private NonVirtualizingLayoutContext _contextAdapter;
+        private NonVirtualizingLayoutContext? _contextAdapter;
 
         /// <summary>
         /// Gets the number of items in the data.
diff --git a/src/Avalonia.Layout/WrapLayout/UvMeasure.cs b/src/Avalonia.Layout/WrapLayout/UvMeasure.cs
index e10e6bd0f8..91fa459acb 100644
--- a/src/Avalonia.Layout/WrapLayout/UvMeasure.cs
+++ b/src/Avalonia.Layout/WrapLayout/UvMeasure.cs
@@ -27,7 +27,7 @@ namespace Avalonia.Layout
             }
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (obj is UvMeasure measure)
             {
diff --git a/src/Avalonia.Layout/WrapLayout/WrapItem.cs b/src/Avalonia.Layout/WrapLayout/WrapItem.cs
index 2f0b39a2d1..e823ade6d4 100644
--- a/src/Avalonia.Layout/WrapLayout/WrapItem.cs
+++ b/src/Avalonia.Layout/WrapLayout/WrapItem.cs
@@ -20,6 +20,6 @@ namespace Avalonia.Layout
 
         public UvMeasure? Position { get; internal set; }
 
-        public ILayoutable Element { get; internal set; }
+        public ILayoutable? Element { get; internal set; }
     }
 }
diff --git a/src/Avalonia.Layout/WrapLayout/WrapLayout.cs b/src/Avalonia.Layout/WrapLayout/WrapLayout.cs
index ded2afc3dd..d12a83d1d7 100644
--- a/src/Avalonia.Layout/WrapLayout/WrapLayout.cs
+++ b/src/Avalonia.Layout/WrapLayout/WrapLayout.cs
@@ -88,7 +88,7 @@ namespace Avalonia.Layout
         /// <inheritdoc />
         protected internal override void OnItemsChangedCore(VirtualizingLayoutContext context, object source, NotifyCollectionChangedEventArgs args)
         {
-            var state = (WrapLayoutState)context.LayoutState;
+            var state = (WrapLayoutState)context.LayoutState!;
 
             switch (args.Action)
             {
@@ -126,7 +126,7 @@ namespace Avalonia.Layout
             var realizationBounds = new UvBounds(Orientation, context.RealizationRect);
             var position = UvMeasure.Zero;
 
-            var state = (WrapLayoutState)context.LayoutState;
+            var state = (WrapLayoutState)context.LayoutState!;
             if (state.Orientation != Orientation)
             {
                 state.SetOrientation(Orientation);
@@ -261,7 +261,7 @@ namespace Avalonia.Layout
                 var spacingMeasure = new UvMeasure(Orientation, HorizontalSpacing, VerticalSpacing);
                 var realizationBounds = new UvBounds(Orientation, context.RealizationRect);
 
-                var state = (WrapLayoutState)context.LayoutState;
+                var state = (WrapLayoutState)context.LayoutState!;
                 bool Arrange(WrapItem item, bool isLast = false)
                 {
                     if (item.Measure.HasValue == false)
diff --git a/src/Avalonia.Layout/WrapLayout/WrapLayoutState.cs b/src/Avalonia.Layout/WrapLayout/WrapLayoutState.cs
index 7955ea983c..720ab96830 100644
--- a/src/Avalonia.Layout/WrapLayout/WrapLayoutState.cs
+++ b/src/Avalonia.Layout/WrapLayout/WrapLayoutState.cs
@@ -62,8 +62,11 @@ namespace Avalonia.Layout
 
         internal void SetOrientation(Orientation orientation)
         {
-            foreach (var item in _items.Where(i => i.Measure.HasValue))
+            foreach (var item in _items)
             {
+                if (!item.Measure.HasValue)
+                    continue;
+
                 UvMeasure measure = item.Measure.Value;
                 double v = measure.V;
                 measure.V = measure.U;
@@ -120,10 +123,10 @@ namespace Avalonia.Layout
                 }
 
                 lastPosition = item.Position;
-                maxV = Math.Max(maxV, item.Measure.Value.V);
+                maxV = Math.Max(maxV, item.Measure!.Value.V);
             }
 
-            double totalHeight = lastPosition.Value.V + maxV;
+            double totalHeight = lastPosition!.Value.V + maxV;
             if (calculateAverage)
             {
                 return (totalHeight / itemCount) * _context.ItemCount;
diff --git a/src/Avalonia.Native/Avalonia.Native.csproj b/src/Avalonia.Native/Avalonia.Native.csproj
index c37bef0488..c1143b7885 100644
--- a/src/Avalonia.Native/Avalonia.Native.csproj
+++ b/src/Avalonia.Native/Avalonia.Native.csproj
@@ -4,7 +4,7 @@
     <PackAvaloniaNative Condition="'$(PackAvaloniaNative)' == ''">$([MSBuild]::IsOSPlatform(OSX))</PackAvaloniaNative>
     <IsPackable>$(PackAvaloniaNative)</IsPackable>
     <IsPackable Condition="'$([MSBuild]::IsOSPlatform(OSX))' == 'True'">true</IsPackable>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
diff --git a/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs b/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs
index b9d8fd3711..bda1c91750 100644
--- a/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs
+++ b/src/Avalonia.Native/AvaloniaNativeMenuExporter.cs
@@ -142,6 +142,13 @@ namespace Avalonia.Native
 
         private void DoLayoutReset(bool forceUpdate = false)
         {
+            var macOpts = AvaloniaLocator.Current.GetService<MacOSPlatformOptions>();
+
+            if (macOpts != null && macOpts.DisableNativeMenus)
+            {
+                return;
+            }
+
             if (_resetQueued || forceUpdate)
             {
                 _resetQueued = false;
diff --git a/src/Avalonia.Native/AvaloniaNativePlatformExtensions.cs b/src/Avalonia.Native/AvaloniaNativePlatformExtensions.cs
index eef765e7ec..10619d675b 100644
--- a/src/Avalonia.Native/AvaloniaNativePlatformExtensions.cs
+++ b/src/Avalonia.Native/AvaloniaNativePlatformExtensions.cs
@@ -73,5 +73,10 @@ namespace Avalonia
         /// You can prevent Avalonia from adding those items to the OSX Application Menu with this property. The default value is false.
         /// </summary>
         public bool DisableDefaultApplicationMenuItems { get; set; }
+        
+        /// <summary>
+        /// Gets or sets a value indicating whether the native macOS menu bar will be enabled for the application.
+        /// </summary>
+        public bool DisableNativeMenus { get; set; }
     }
 }
diff --git a/src/Avalonia.OpenGL/Avalonia.OpenGL.csproj b/src/Avalonia.OpenGL/Avalonia.OpenGL.csproj
index 5649d46102..2b32926008 100644
--- a/src/Avalonia.OpenGL/Avalonia.OpenGL.csproj
+++ b/src/Avalonia.OpenGL/Avalonia.OpenGL.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     </PropertyGroup>
 
diff --git a/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj b/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj
index 189b156569..348f5f3a10 100644
--- a/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj
+++ b/src/Avalonia.ReactiveUI/Avalonia.ReactiveUI.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <PackageId>Avalonia.ReactiveUI</PackageId>
     <SignAssembly>false</SignAssembly>
   </PropertyGroup>
diff --git a/src/Avalonia.Remote.Protocol/Avalonia.Remote.Protocol.csproj b/src/Avalonia.Remote.Protocol/Avalonia.Remote.Protocol.csproj
index 3be0a688ab..5a8301a2e9 100644
--- a/src/Avalonia.Remote.Protocol/Avalonia.Remote.Protocol.csproj
+++ b/src/Avalonia.Remote.Protocol/Avalonia.Remote.Protocol.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <DefineConstants>AVALONIA_REMOTE_PROTOCOL;$(DefineConstants)</DefineConstants>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Key.snk</AssemblyOriginatorKeyFile>
diff --git a/src/Avalonia.Styling/Avalonia.Styling.csproj b/src/Avalonia.Styling/Avalonia.Styling.csproj
index 20b3183b00..139ba1bd2e 100644
--- a/src/Avalonia.Styling/Avalonia.Styling.csproj
+++ b/src/Avalonia.Styling/Avalonia.Styling.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <AssemblyName>Avalonia.Styling</AssemblyName>
     <RootNamespace>Avalonia</RootNamespace>
   </PropertyGroup>
@@ -9,4 +9,5 @@
     <ProjectReference Include="..\Avalonia.Base\Avalonia.Base.csproj" />
   </ItemGroup>
   <Import Project="..\..\build\ApiDiff.props" />
+  <Import Project="..\..\build\NullableEnable.props" />
 </Project>
diff --git a/src/Avalonia.Styling/Controls/ChildNameScope.cs b/src/Avalonia.Styling/Controls/ChildNameScope.cs
index e6707e71db..58114a57fd 100644
--- a/src/Avalonia.Styling/Controls/ChildNameScope.cs
+++ b/src/Avalonia.Styling/Controls/ChildNameScope.cs
@@ -15,20 +15,20 @@ namespace Avalonia.Controls
         
         public void Register(string name, object element) => _inner.Register(name, element);
 
-        public SynchronousCompletionAsyncResult<object> FindAsync(string name)
+        public SynchronousCompletionAsyncResult<object?> FindAsync(string name)
         {
             var found = Find(name);
             if (found != null)
-                return new SynchronousCompletionAsyncResult<object>(found);
+                return new SynchronousCompletionAsyncResult<object?>(found);
             // Not found and both current and parent scope are in completed state
             if(IsCompleted)
-                return new SynchronousCompletionAsyncResult<object>(null);
+                return new SynchronousCompletionAsyncResult<object?>(null);
             return DoFindAsync(name);
         }
 
-        public SynchronousCompletionAsyncResult<object> DoFindAsync(string name)
+        public SynchronousCompletionAsyncResult<object?> DoFindAsync(string name)
         {
-            var src = new SynchronousCompletionAsyncResultSource<object>();
+            var src = new SynchronousCompletionAsyncResultSource<object?>();
 
             void ParentSearch()
             {
@@ -56,7 +56,7 @@ namespace Avalonia.Controls
             return src.AsyncResult;
         }
 
-        public object Find(string name)
+        public object? Find(string name)
         {
             var found = _inner.Find(name);
             if (found != null)
diff --git a/src/Avalonia.Styling/Controls/INameScope.cs b/src/Avalonia.Styling/Controls/INameScope.cs
index 2d5295fe45..1ca7db2f37 100644
--- a/src/Avalonia.Styling/Controls/INameScope.cs
+++ b/src/Avalonia.Styling/Controls/INameScope.cs
@@ -22,14 +22,14 @@ namespace Avalonia.Controls
         /// </summary>
         /// <param name="name">The name.</param>
         /// <returns>The element, or null if the name was not found.</returns>
-        SynchronousCompletionAsyncResult<object> FindAsync(string name);
+        SynchronousCompletionAsyncResult<object?> FindAsync(string name);
         
         /// <summary>
         /// Finds a named element in the name scope, returns immediately, doesn't traverse the name scope stack
         /// </summary>
         /// <param name="name">The name.</param>
         /// <returns>The element, or null if the name was not found.</returns>
-        object Find(string name);
+        object? Find(string name);
 
         /// <summary>
         /// Marks the name scope as completed, no further registrations will be allowed
diff --git a/src/Avalonia.Styling/Controls/NameScope.cs b/src/Avalonia.Styling/Controls/NameScope.cs
index 62a04eac8b..77f98f85c4 100644
--- a/src/Avalonia.Styling/Controls/NameScope.cs
+++ b/src/Avalonia.Styling/Controls/NameScope.cs
@@ -22,8 +22,8 @@ namespace Avalonia.Controls
         
         private readonly Dictionary<string, object> _inner = new Dictionary<string, object>();
 
-        private readonly Dictionary<string, SynchronousCompletionAsyncResultSource<object>> _pendingSearches =
-            new Dictionary<string, SynchronousCompletionAsyncResultSource<object>>();
+        private readonly Dictionary<string, SynchronousCompletionAsyncResultSource<object?>> _pendingSearches =
+            new Dictionary<string, SynchronousCompletionAsyncResultSource<object?>>();
         
         /// <summary>
         /// Gets the value of the attached <see cref="NameScopeProperty"/> on a styled element.
@@ -32,7 +32,7 @@ namespace Avalonia.Controls
         /// <returns>The value of the NameScope attached property.</returns>
         public static INameScope GetNameScope(StyledElement styled)
         {
-            Contract.Requires<ArgumentNullException>(styled != null);
+            _ = styled ?? throw new ArgumentNullException(nameof(styled));
 
             return styled.GetValue(NameScopeProperty);
         }
@@ -44,7 +44,7 @@ namespace Avalonia.Controls
         /// <param name="value">The value to set.</param>
         public static void SetNameScope(StyledElement styled, INameScope value)
         {
-            Contract.Requires<ArgumentNullException>(styled != null);
+            _ = styled ?? throw new ArgumentNullException(nameof(styled));
 
             styled.SetValue(NameScopeProperty, value);
         }
@@ -54,12 +54,11 @@ namespace Avalonia.Controls
         {
             if (IsCompleted)
                 throw new InvalidOperationException("NameScope is completed, no further registrations are allowed");
-            Contract.Requires<ArgumentNullException>(name != null);
-            Contract.Requires<ArgumentNullException>(element != null);
 
-            object existing;
+            _ = name ?? throw new ArgumentNullException(nameof(name));
+            _ = element ?? throw new ArgumentNullException(nameof(element));
 
-            if (_inner.TryGetValue(name, out existing))
+            if (_inner.TryGetValue(name, out var existing))
             {
                 if (existing != element)
                 {
@@ -77,27 +76,26 @@ namespace Avalonia.Controls
             }
         }
 
-        public SynchronousCompletionAsyncResult<object> FindAsync(string name)
+        public SynchronousCompletionAsyncResult<object?> FindAsync(string name)
         {
             var found = Find(name);
             if (found != null)
-                return new SynchronousCompletionAsyncResult<object>(found);
+                return new SynchronousCompletionAsyncResult<object?>(found);
             if (IsCompleted)
-                return new SynchronousCompletionAsyncResult<object>((object)null);
+                return new SynchronousCompletionAsyncResult<object?>(null);
             if (!_pendingSearches.TryGetValue(name, out var tcs))
                 // We are intentionally running continuations synchronously here
-                _pendingSearches[name] = tcs = new SynchronousCompletionAsyncResultSource<object>();
+                _pendingSearches[name] = tcs = new SynchronousCompletionAsyncResultSource<object?>();
 
             return tcs.AsyncResult;
         }
 
         /// <inheritdoc />
-        public object Find(string name)
+        public object? Find(string name)
         {
-            Contract.Requires<ArgumentNullException>(name != null);
+            _ = name ?? throw new ArgumentNullException(nameof(name));
 
-            object result;
-            _inner.TryGetValue(name, out result);
+            _inner.TryGetValue(name, out var result);
             return result;
         }
 
diff --git a/src/Avalonia.Styling/Controls/NameScopeExtensions.cs b/src/Avalonia.Styling/Controls/NameScopeExtensions.cs
index 75630711b8..3895b6ceb9 100644
--- a/src/Avalonia.Styling/Controls/NameScopeExtensions.cs
+++ b/src/Avalonia.Styling/Controls/NameScopeExtensions.cs
@@ -17,11 +17,11 @@ namespace Avalonia.Controls
         /// <param name="nameScope">The name scope.</param>
         /// <param name="name">The name.</param>
         /// <returns>The named element or null if not found.</returns>
-        public static T Find<T>(this INameScope nameScope, string name)
+        public static T? Find<T>(this INameScope nameScope, string name)
             where T : class
         {
-            Contract.Requires<ArgumentNullException>(nameScope != null);
-            Contract.Requires<ArgumentNullException>(name != null);
+            _ = nameScope ?? throw new ArgumentNullException(nameof(nameScope));
+            _ = name ?? throw new ArgumentNullException(nameof(name));
 
             var result = nameScope.Find(name);
 
@@ -31,7 +31,7 @@ namespace Avalonia.Controls
                     $"Expected control '{name}' to be '{typeof(T)} but it was '{result.GetType()}'.");
             }
 
-            return (T)result;
+            return (T?)result;
         }
 
         /// <summary>
@@ -41,11 +41,11 @@ namespace Avalonia.Controls
         /// <param name="anchor">The control to take the name scope from.</param>
         /// <param name="name">The name.</param>
         /// <returns>The named element or null if not found.</returns>
-        public static T Find<T>(this ILogical anchor, string name)
+        public static T? Find<T>(this ILogical anchor, string name)
             where T : class
         {
-            Contract.Requires<ArgumentNullException>(anchor != null);
-            Contract.Requires<ArgumentNullException>(name != null);
+            _ = anchor ?? throw new ArgumentNullException(nameof(anchor));
+            _ = name ?? throw new ArgumentNullException(nameof(name));
             var styledAnchor = anchor as StyledElement;
             if (styledAnchor == null)
                 return null;
@@ -64,8 +64,8 @@ namespace Avalonia.Controls
         public static T Get<T>(this INameScope nameScope, string name)
             where T : class
         {
-            Contract.Requires<ArgumentNullException>(nameScope != null);
-            Contract.Requires<ArgumentNullException>(name != null);
+            _ = nameScope ?? throw new ArgumentNullException(nameof(nameScope));
+            _ = name ?? throw new ArgumentNullException(nameof(name));
 
             var result = nameScope.Find(name);
 
@@ -94,9 +94,9 @@ namespace Avalonia.Controls
         public static T Get<T>(this ILogical anchor, string name)
             where T : class
         {
-            Contract.Requires<ArgumentNullException>(anchor != null);
-            Contract.Requires<ArgumentNullException>(name != null);
-               
+            _ = anchor ?? throw new ArgumentNullException(nameof(anchor));
+            _ = name ?? throw new ArgumentNullException(nameof(name));
+
             var nameScope = (anchor as INameScope) ?? NameScope.GetNameScope((StyledElement)anchor);
             if (nameScope == null)
                 throw new InvalidOperationException(
@@ -105,9 +105,9 @@ namespace Avalonia.Controls
             return nameScope.Get<T>(name);
         }
         
-        public static INameScope FindNameScope(this ILogical control)
+        public static INameScope? FindNameScope(this ILogical control)
         {
-            Contract.Requires<ArgumentNullException>(control != null);
+            _ = control ?? throw new ArgumentNullException(nameof(control));
 
             var scope = control.GetSelfAndLogicalAncestors()
                 .OfType<StyledElement>()
diff --git a/src/Avalonia.Styling/Controls/NameScopeLocator.cs b/src/Avalonia.Styling/Controls/NameScopeLocator.cs
index 51f4c5c4eb..f0ce7f8a5b 100644
--- a/src/Avalonia.Styling/Controls/NameScopeLocator.cs
+++ b/src/Avalonia.Styling/Controls/NameScopeLocator.cs
@@ -11,9 +11,9 @@ namespace Avalonia.Controls
         /// </summary>
         /// <param name="scope">The scope relative from which the object should be resolved.</param>
         /// <param name="name">The name of the object to find.</param>
-        public static IObservable<object> Track(INameScope scope, string name)
+        public static IObservable<object?> Track(INameScope scope, string name)
         {
-            return new NeverEndingSynchronousCompletionAsyncResultObservable<object>(scope.FindAsync(name));
+            return new NeverEndingSynchronousCompletionAsyncResultObservable<object?>(scope.FindAsync(name));
         }
         
         // This class is implemented in such weird way because for some reason
@@ -22,7 +22,7 @@ namespace Avalonia.Controls
 
         private class NeverEndingSynchronousCompletionAsyncResultObservable<T> : IObservable<T>
         {
-            private T _value;
+            private T? _value;
             private SynchronousCompletionAsyncResult<T>? _asyncResult;
 
             public NeverEndingSynchronousCompletionAsyncResultObservable(SynchronousCompletionAsyncResult<T> task)
@@ -47,7 +47,7 @@ namespace Avalonia.Controls
                         observer.OnNext(_asyncResult.Value.GetResult());
                     });
                 else
-                    observer.OnNext(_value);
+                    observer.OnNext(_value!);
                 
                 return Disposable.Empty;
             }
diff --git a/src/Avalonia.Styling/Controls/PseudoClassesExtensions.cs b/src/Avalonia.Styling/Controls/PseudoClassesExtensions.cs
index 7b28d1a911..4cddc8c8fb 100644
--- a/src/Avalonia.Styling/Controls/PseudoClassesExtensions.cs
+++ b/src/Avalonia.Styling/Controls/PseudoClassesExtensions.cs
@@ -12,7 +12,7 @@ namespace Avalonia.Controls
         /// <param name="value">True to add the pseudoclass or false to remove.</param>
         public static void Set(this IPseudoClasses classes, string name, bool value)
         {
-            Contract.Requires<ArgumentNullException>(classes != null);
+            _ = classes ?? throw new ArgumentNullException(nameof(classes));
 
             if (value)
             {
diff --git a/src/Avalonia.Styling/Controls/ResourceDictionary.cs b/src/Avalonia.Styling/Controls/ResourceDictionary.cs
index e797f8cf8b..3af14daa83 100644
--- a/src/Avalonia.Styling/Controls/ResourceDictionary.cs
+++ b/src/Avalonia.Styling/Controls/ResourceDictionary.cs
@@ -177,7 +177,7 @@ namespace Avalonia.Controls
             }
         }
 
-        private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void OnCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             Owner?.NotifyHostedResourcesChanged(ResourcesChangedEventArgs.Empty);
         }
diff --git a/src/Avalonia.Styling/Controls/ResourceNodeExtensions.cs b/src/Avalonia.Styling/Controls/ResourceNodeExtensions.cs
index be1069a4da..513b3f2424 100644
--- a/src/Avalonia.Styling/Controls/ResourceNodeExtensions.cs
+++ b/src/Avalonia.Styling/Controls/ResourceNodeExtensions.cs
@@ -109,7 +109,7 @@ namespace Avalonia.Controls
                 observer.OnNext(Convert(_target.FindResource(_key)));
             }
 
-            private void ResourcesChanged(object sender, ResourcesChangedEventArgs e)
+            private void ResourcesChanged(object? sender, ResourcesChangedEventArgs e)
             {
                 PublishNext(Convert(_target.FindResource(_key)));
             }
@@ -159,7 +159,7 @@ namespace Avalonia.Controls
                 }
             }
 
-            private void OwnerChanged(object sender, EventArgs e)
+            private void OwnerChanged(object? sender, EventArgs e)
             {
                 if (_owner is object)
                 {
@@ -176,7 +176,7 @@ namespace Avalonia.Controls
                 PublishNext();
             }
 
-            private void ResourcesChanged(object sender, ResourcesChangedEventArgs e)
+            private void ResourcesChanged(object? sender, ResourcesChangedEventArgs e)
             {
                 PublishNext();
             }
diff --git a/src/Avalonia.Styling/INamed.cs b/src/Avalonia.Styling/INamed.cs
index 1f8d269b07..df83f3b6ef 100644
--- a/src/Avalonia.Styling/INamed.cs
+++ b/src/Avalonia.Styling/INamed.cs
@@ -8,6 +8,6 @@ namespace Avalonia
         /// <summary>
         /// Gets the element name.
         /// </summary>
-        string Name { get; }
+        string? Name { get; }
     }
 }
diff --git a/src/Avalonia.Styling/LogicalTree/ControlLocator.cs b/src/Avalonia.Styling/LogicalTree/ControlLocator.cs
index 6d0302ace4..f60ed5aab8 100644
--- a/src/Avalonia.Styling/LogicalTree/ControlLocator.cs
+++ b/src/Avalonia.Styling/LogicalTree/ControlLocator.cs
@@ -9,19 +9,19 @@ namespace Avalonia.LogicalTree
     /// </summary>
     public static class ControlLocator
     {
-        public static IObservable<ILogical> Track(ILogical relativeTo, int ancestorLevel, Type ancestorType = null)
+        public static IObservable<ILogical?> Track(ILogical relativeTo, int ancestorLevel, Type? ancestorType = null)
         {
             return new ControlTracker(relativeTo, ancestorLevel, ancestorType);
         }
 
-        private class ControlTracker : LightweightObservableBase<ILogical>
+        private class ControlTracker : LightweightObservableBase<ILogical?>
         {
             private readonly ILogical _relativeTo;
             private readonly int _ancestorLevel;
-            private readonly Type _ancestorType;
-            private ILogical _value;
+            private readonly Type? _ancestorType;
+            private ILogical? _value;
 
-            public ControlTracker(ILogical relativeTo, int ancestorLevel, Type ancestorType)
+            public ControlTracker(ILogical relativeTo, int ancestorLevel, Type? ancestorType)
             {
                 _relativeTo = relativeTo;
                 _ancestorLevel = ancestorLevel;
@@ -43,18 +43,18 @@ namespace Avalonia.LogicalTree
                 _value = null;
             }
 
-            protected override void Subscribed(IObserver<ILogical> observer, bool first)
+            protected override void Subscribed(IObserver<ILogical?> observer, bool first)
             {
                 observer.OnNext(_value);
             }
 
-            private void Attached(object sender, LogicalTreeAttachmentEventArgs e)
+            private void Attached(object? sender, LogicalTreeAttachmentEventArgs e)
             {
                 Update();
                 PublishNext(_value);
             }
 
-            private void Detached(object sender, LogicalTreeAttachmentEventArgs e)
+            private void Detached(object? sender, LogicalTreeAttachmentEventArgs e)
             {
                 _value = null;
                 PublishNext(null);
diff --git a/src/Avalonia.Styling/LogicalTree/ILogical.cs b/src/Avalonia.Styling/LogicalTree/ILogical.cs
index 9c4223618f..caff3d8150 100644
--- a/src/Avalonia.Styling/LogicalTree/ILogical.cs
+++ b/src/Avalonia.Styling/LogicalTree/ILogical.cs
@@ -12,12 +12,12 @@ namespace Avalonia.LogicalTree
         /// <summary>
         /// Raised when the control is attached to a rooted logical tree.
         /// </summary>
-        event EventHandler<LogicalTreeAttachmentEventArgs> AttachedToLogicalTree;
+        event EventHandler<LogicalTreeAttachmentEventArgs>? AttachedToLogicalTree;
 
         /// <summary>
         /// Raised when the control is detached from a rooted logical tree.
         /// </summary>
-        event EventHandler<LogicalTreeAttachmentEventArgs> DetachedFromLogicalTree;
+        event EventHandler<LogicalTreeAttachmentEventArgs>? DetachedFromLogicalTree;
 
         /// <summary>
         /// Gets a value indicating whether the element is attached to a rooted logical tree.
@@ -27,7 +27,7 @@ namespace Avalonia.LogicalTree
         /// <summary>
         /// Gets the logical parent.
         /// </summary>
-        ILogical LogicalParent { get; }
+        ILogical? LogicalParent { get; }
 
         /// <summary>
         /// Gets the logical children.
diff --git a/src/Avalonia.Styling/LogicalTree/LogicalExtensions.cs b/src/Avalonia.Styling/LogicalTree/LogicalExtensions.cs
index 458ab0fce2..74720c0a77 100644
--- a/src/Avalonia.Styling/LogicalTree/LogicalExtensions.cs
+++ b/src/Avalonia.Styling/LogicalTree/LogicalExtensions.cs
@@ -15,14 +15,14 @@ namespace Avalonia.LogicalTree
         /// <returns>The logical's ancestors.</returns>
         public static IEnumerable<ILogical> GetLogicalAncestors(this ILogical logical)
         {
-            Contract.Requires<ArgumentNullException>(logical != null);
+            _ = logical ?? throw new ArgumentNullException(nameof(logical));
 
-            logical = logical.LogicalParent;
+            ILogical? l = logical.LogicalParent;
 
-            while (logical != null)
+            while (l != null)
             {
-                yield return logical;
-                logical = logical.LogicalParent;
+                yield return l;
+                l = l.LogicalParent;
             }
         }
 
@@ -48,14 +48,14 @@ namespace Avalonia.LogicalTree
         /// <param name="logical">The logical.</param>
         /// <param name="includeSelf">If given logical should be included in search.</param>
         /// <returns>First ancestor of given type.</returns>
-        public static T FindLogicalAncestorOfType<T>(this ILogical logical, bool includeSelf = false) where T : class
+        public static T? FindLogicalAncestorOfType<T>(this ILogical logical, bool includeSelf = false) where T : class
         {
             if (logical is null)
             {
                 return null;
             }
 
-            ILogical parent = includeSelf ? logical : logical.LogicalParent;
+            var parent = includeSelf ? logical : logical.LogicalParent;
 
             while (parent != null)
             {
@@ -120,7 +120,7 @@ namespace Avalonia.LogicalTree
         /// <param name="logical">The logical.</param>
         /// <param name="includeSelf">If given logical should be included in search.</param>
         /// <returns>First descendant of given type.</returns>
-        public static T FindLogicalDescendantOfType<T>(this ILogical logical, bool includeSelf = false) where T : class
+        public static T? FindLogicalDescendantOfType<T>(this ILogical logical, bool includeSelf = false) where T : class
         {
             if (logical is null)
             {
@@ -140,7 +140,7 @@ namespace Avalonia.LogicalTree
         /// </summary>
         /// <param name="logical">The logical.</param>
         /// <returns>The parent, or null if the logical is unparented.</returns>
-        public static ILogical GetLogicalParent(this ILogical logical)
+        public static ILogical? GetLogicalParent(this ILogical logical)
         {
             return logical.LogicalParent;
         }
@@ -153,7 +153,7 @@ namespace Avalonia.LogicalTree
         /// <returns>
         /// The parent, or null if the logical is unparented or its parent is not of type <typeparamref name="T"/>.
         /// </returns>
-        public static T GetLogicalParent<T>(this ILogical logical) where T : class
+        public static T? GetLogicalParent<T>(this ILogical logical) where T : class
         {
             return logical.LogicalParent as T;
         }
@@ -165,7 +165,7 @@ namespace Avalonia.LogicalTree
         /// <returns>The logical siblings.</returns>
         public static IEnumerable<ILogical> GetLogicalSiblings(this ILogical logical)
         {
-            ILogical parent = logical.LogicalParent;
+            var parent = logical.LogicalParent;
 
             if (parent != null)
             {
@@ -187,7 +187,7 @@ namespace Avalonia.LogicalTree
         /// </returns>
         public static bool IsLogicalAncestorOf(this ILogical logical, ILogical target)
         {
-            ILogical current = target?.LogicalParent;
+            var current = target?.LogicalParent;
 
             while (current != null)
             {
@@ -202,7 +202,7 @@ namespace Avalonia.LogicalTree
             return false;
         }
 
-        private static T FindDescendantOfTypeCore<T>(ILogical logical) where T : class
+        private static T? FindDescendantOfTypeCore<T>(ILogical logical) where T : class
         {
             var logicalChildren = logical.LogicalChildren;
             var logicalChildrenCount = logicalChildren.Count;
diff --git a/src/Avalonia.Styling/LogicalTree/LogicalTreeAttachmentEventArgs.cs b/src/Avalonia.Styling/LogicalTree/LogicalTreeAttachmentEventArgs.cs
index 891724599c..826fc5b2a4 100644
--- a/src/Avalonia.Styling/LogicalTree/LogicalTreeAttachmentEventArgs.cs
+++ b/src/Avalonia.Styling/LogicalTree/LogicalTreeAttachmentEventArgs.cs
@@ -19,11 +19,8 @@ namespace Avalonia.LogicalTree
             ILogical source,
             ILogical parent)
         {
-            Contract.Requires<ArgumentNullException>(root != null);
-            Contract.Requires<ArgumentNullException>(source != null);
-
-            Root = root;
-            Source = source;
+            Root = root ?? throw new ArgumentNullException(nameof(root));
+            Source = source ?? throw new ArgumentNullException(nameof(source));
             Parent = parent;
         }
 
diff --git a/src/Avalonia.Styling/StyledElement.cs b/src/Avalonia.Styling/StyledElement.cs
index 2292f5c518..5f498623e1 100644
--- a/src/Avalonia.Styling/StyledElement.cs
+++ b/src/Avalonia.Styling/StyledElement.cs
@@ -427,7 +427,7 @@ namespace Avalonia
 
                 if (_logicalRoot != null)
                 {
-                    var e = new LogicalTreeAttachmentEventArgs(_logicalRoot, this, old);
+                    var e = new LogicalTreeAttachmentEventArgs(_logicalRoot, this, old!);
                     OnDetachedFromLogicalTreeCore(e);
                 }
 
@@ -435,7 +435,7 @@ namespace Avalonia
 
                 if (newRoot is object)
                 {
-                    var e = new LogicalTreeAttachmentEventArgs(newRoot, this, parent);
+                    var e = new LogicalTreeAttachmentEventArgs(newRoot, this, parent!);
                     OnAttachedToLogicalTreeCore(e);
                 }
                 else if (parent is null)
@@ -495,21 +495,21 @@ namespace Avalonia
             DetachStylesFromThisAndDescendents(allStyles);
         }
 
-        protected virtual void LogicalChildrenCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        protected virtual void LogicalChildrenCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             switch (e.Action)
             {
                 case NotifyCollectionChangedAction.Add:
-                    SetLogicalParent(e.NewItems);
+                    SetLogicalParent(e.NewItems!);
                     break;
 
                 case NotifyCollectionChangedAction.Remove:
-                    ClearLogicalParent(e.OldItems);
+                    ClearLogicalParent(e.OldItems!);
                     break;
 
                 case NotifyCollectionChangedAction.Replace:
-                    ClearLogicalParent(e.OldItems);
-                    SetLogicalParent(e.NewItems);
+                    ClearLogicalParent(e.OldItems!);
+                    SetLogicalParent(e.NewItems!);
                     break;
 
                 case NotifyCollectionChangedAction.Reset:
@@ -729,7 +729,7 @@ namespace Avalonia
 
             for (var i = 0; i < count; i++)
             {
-                var logical = (ILogical) children[i];
+                var logical = (ILogical) children[i]!;
                 
                 if (logical.LogicalParent is null)
                 {
@@ -744,7 +744,7 @@ namespace Avalonia
 
             for (var i = 0; i < count; i++)
             {
-                var logical = (ILogical) children[i];
+                var logical = (ILogical) children[i]!;
                 
                 if (logical.LogicalParent == this)
                 {
diff --git a/src/Avalonia.Styling/Styling/Activators/NthChildActivator.cs b/src/Avalonia.Styling/Styling/Activators/NthChildActivator.cs
index 803809a8ce..6f54cd5904 100644
--- a/src/Avalonia.Styling/Styling/Activators/NthChildActivator.cs
+++ b/src/Avalonia.Styling/Styling/Activators/NthChildActivator.cs
@@ -37,7 +37,7 @@ namespace Avalonia.Styling.Activators
             _provider.ChildIndexChanged -= ChildIndexChanged;
         }
 
-        private void ChildIndexChanged(object sender, ChildIndexChangedEventArgs e)
+        private void ChildIndexChanged(object? sender, ChildIndexChangedEventArgs e)
         {
             // Run matching again if:
             // 1. Selector is reversed, so other item insertion/deletion might affect total count without changing subscribed item index.
diff --git a/src/Avalonia.Styling/Styling/Activators/StyleClassActivator.cs b/src/Avalonia.Styling/Styling/Activators/StyleClassActivator.cs
index 7906a29cb5..98d3f16a0a 100644
--- a/src/Avalonia.Styling/Styling/Activators/StyleClassActivator.cs
+++ b/src/Avalonia.Styling/Styling/Activators/StyleClassActivator.cs
@@ -66,7 +66,7 @@ namespace Avalonia.Styling.Activators
             _classes.CollectionChanged -= ClassesChangedHandler;
         }
 
-        private void ClassesChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void ClassesChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             if (e.Action != NotifyCollectionChangedAction.Move)
             {
diff --git a/src/Avalonia.Styling/Styling/ChildSelector.cs b/src/Avalonia.Styling/Styling/ChildSelector.cs
index 85e7aaabde..5c92182b80 100644
--- a/src/Avalonia.Styling/Styling/ChildSelector.cs
+++ b/src/Avalonia.Styling/Styling/ChildSelector.cs
@@ -6,7 +6,7 @@ namespace Avalonia.Styling
     internal class ChildSelector : Selector
     {
         private readonly Selector _parent;
-        private string _selectorString;
+        private string? _selectorString;
 
         public ChildSelector(Selector parent)
         {
@@ -25,7 +25,7 @@ namespace Avalonia.Styling
         public override bool IsCombinator => true;
 
         /// <inheritdoc/>
-        public override Type TargetType => null;
+        public override Type? TargetType => null;
 
         public override string ToString()
         {
@@ -64,6 +64,6 @@ namespace Avalonia.Styling
             }
         }
 
-        protected override Selector MovePrevious() => null;
+        protected override Selector? MovePrevious() => null;
     }
 }
diff --git a/src/Avalonia.Styling/Styling/OrSelector.cs b/src/Avalonia.Styling/Styling/OrSelector.cs
index 8251915504..3d6db9b01e 100644
--- a/src/Avalonia.Styling/Styling/OrSelector.cs
+++ b/src/Avalonia.Styling/Styling/OrSelector.cs
@@ -120,7 +120,7 @@ namespace Avalonia.Styling
                 }
                 else
                 {
-                    while (!result.IsAssignableFrom(selector.TargetType))
+                    while (result is not null && !result.IsAssignableFrom(selector.TargetType))
                     {
                         result = result.BaseType;
                     }
diff --git a/src/Avalonia.Styling/Styling/PropertyEqualsSelector.cs b/src/Avalonia.Styling/Styling/PropertyEqualsSelector.cs
index a531267eea..1cd1a650ef 100644
--- a/src/Avalonia.Styling/Styling/PropertyEqualsSelector.cs
+++ b/src/Avalonia.Styling/Styling/PropertyEqualsSelector.cs
@@ -53,11 +53,16 @@ namespace Avalonia.Styling
 
                 if (_property.IsAttached)
                 {
+                    builder.Append('(');
                     builder.Append(_property.OwnerType.Name);
                     builder.Append('.');
                 }
 
                 builder.Append(_property.Name);
+                if (_property.IsAttached)
+                {
+                    builder.Append(')');
+                }
                 builder.Append('=');
                 builder.Append(_value ?? string.Empty);
                 builder.Append(']');
@@ -104,7 +109,7 @@ namespace Avalonia.Styling
             var converter = TypeDescriptor.GetConverter(propertyType);
             if (converter?.CanConvertFrom(valueType) == true)
             {
-                return Equals(propertyValue, converter.ConvertFrom(null, CultureInfo.InvariantCulture, value));
+                return Equals(propertyValue, converter.ConvertFrom(null, CultureInfo.InvariantCulture, value!));
             }
 
             return false;
diff --git a/src/Avalonia.Styling/Styling/Selectors.cs b/src/Avalonia.Styling/Styling/Selectors.cs
index 64d0a0e96b..7c66469cf1 100644
--- a/src/Avalonia.Styling/Styling/Selectors.cs
+++ b/src/Avalonia.Styling/Styling/Selectors.cs
@@ -25,10 +25,14 @@ namespace Avalonia.Styling
         /// <param name="previous">The previous selector.</param>
         /// <param name="name">The name of the style class.</param>
         /// <returns>The selector.</returns>
-        public static Selector Class(this Selector previous, string name)
+        public static Selector Class(this Selector? previous, string name)
         {
-            Contract.Requires<ArgumentNullException>(name != null);
-            Contract.Requires<ArgumentException>(!string.IsNullOrWhiteSpace(name));
+            _ = name ?? throw new ArgumentNullException(nameof(name));
+
+            if (string.IsNullOrWhiteSpace(name))
+            {
+                throw new ArgumentException("Name may not be empty", nameof(name));
+            }
 
             var tac = previous as TypeNameAndClassSelector;
 
@@ -48,7 +52,7 @@ namespace Avalonia.Styling
         /// </summary>
         /// <param name="previous">The previous selector.</param>
         /// <returns>The selector.</returns>
-        public static Selector Descendant(this Selector previous)
+        public static Selector Descendant(this Selector? previous)
         {
             return new DescendantSelector(previous);
         }
@@ -59,9 +63,9 @@ namespace Avalonia.Styling
         /// <param name="previous">The previous selector.</param>
         /// <param name="type">The type.</param>
         /// <returns>The selector.</returns>
-        public static Selector Is(this Selector previous, Type type)
+        public static Selector Is(this Selector? previous, Type type)
         {
-            Contract.Requires<ArgumentNullException>(type != null);
+            _ = type ?? throw new ArgumentNullException(nameof(type));
 
             return TypeNameAndClassSelector.Is(previous, type);
         }
@@ -72,7 +76,7 @@ namespace Avalonia.Styling
         /// <typeparam name="T">The type.</typeparam>
         /// <param name="previous">The previous selector.</param>
         /// <returns>The selector.</returns>
-        public static Selector Is<T>(this Selector previous) where T : IStyleable
+        public static Selector Is<T>(this Selector? previous) where T : IStyleable
         {
             return previous.Is(typeof(T));
         }
@@ -83,10 +87,14 @@ namespace Avalonia.Styling
         /// <param name="previous">The previous selector.</param>
         /// <param name="name">The name.</param>
         /// <returns>The selector.</returns>
-        public static Selector Name(this Selector previous, string name)
+        public static Selector Name(this Selector? previous, string name)
         {
-            Contract.Requires<ArgumentNullException>(name != null);
-            Contract.Requires<ArgumentException>(!string.IsNullOrWhiteSpace(name));
+            _ = name ?? throw new ArgumentNullException(nameof(name));
+
+            if (string.IsNullOrWhiteSpace(name))
+            {
+                throw new ArgumentException("Name may not be empty", nameof(name));
+            }
 
             var tac = previous as TypeNameAndClassSelector;
 
@@ -107,7 +115,7 @@ namespace Avalonia.Styling
         /// <param name="previous">The previous selector.</param>
         /// <param name="argument">The selector to be not-ed.</param>
         /// <returns>The selector.</returns>
-        public static Selector Not(this Selector previous, Func<Selector, Selector> argument)
+        public static Selector Not(this Selector? previous, Func<Selector?, Selector> argument)
         {
             return new NotSelector(previous, argument(null));
         }
@@ -118,7 +126,7 @@ namespace Avalonia.Styling
         /// <param name="previous">The previous selector.</param>
         /// <param name="argument">The selector to be not-ed.</param>
         /// <returns>The selector.</returns>
-        public static Selector Not(this Selector previous, Selector argument)
+        public static Selector Not(this Selector? previous, Selector argument)
         {
             return new NotSelector(previous, argument);
         }
@@ -126,7 +134,7 @@ namespace Avalonia.Styling
         /// <inheritdoc cref="NthChildSelector"/>
         /// <inheritdoc cref="NthChildSelector(Selector?, int, int)"/>
         /// <returns>The selector.</returns>
-        public static Selector NthChild(this Selector previous, int step, int offset)
+        public static Selector NthChild(this Selector? previous, int step, int offset)
         {
             return new NthChildSelector(previous, step, offset);
         }
@@ -134,7 +142,7 @@ namespace Avalonia.Styling
         /// <inheritdoc cref="NthLastChildSelector"/>
         /// <inheritdoc cref="NthLastChildSelector(Selector?, int, int)"/>
         /// <returns>The selector.</returns>
-        public static Selector NthLastChild(this Selector previous, int step, int offset)
+        public static Selector NthLastChild(this Selector? previous, int step, int offset)
         {
             return new NthLastChildSelector(previous, step, offset);
         }
@@ -145,9 +153,9 @@ namespace Avalonia.Styling
         /// <param name="previous">The previous selector.</param>
         /// <param name="type">The type.</param>
         /// <returns>The selector.</returns>
-        public static Selector OfType(this Selector previous, Type type)
+        public static Selector OfType(this Selector? previous, Type type)
         {
-            Contract.Requires<ArgumentNullException>(type != null);
+            _ = type ?? throw new ArgumentNullException(nameof(type));
 
             return TypeNameAndClassSelector.OfType(previous, type);
         }
@@ -158,7 +166,7 @@ namespace Avalonia.Styling
         /// <typeparam name="T">The type.</typeparam>
         /// <param name="previous">The previous selector.</param>
         /// <returns>The selector.</returns>
-        public static Selector OfType<T>(this Selector previous) where T : IStyleable
+        public static Selector OfType<T>(this Selector? previous) where T : IStyleable
         {
             return previous.OfType(typeof(T));
         }
@@ -191,9 +199,9 @@ namespace Avalonia.Styling
         /// <param name="property">The property.</param>
         /// <param name="value">The property value.</param>
         /// <returns>The selector.</returns>
-        public static Selector PropertyEquals<T>(this Selector previous, AvaloniaProperty<T> property, object value)
+        public static Selector PropertyEquals<T>(this Selector? previous, AvaloniaProperty<T> property, object? value)
         {
-            Contract.Requires<ArgumentNullException>(property != null);
+            _ = property ?? throw new ArgumentNullException(nameof(property));
 
             return new PropertyEqualsSelector(previous, property, value);
         }
@@ -205,9 +213,9 @@ namespace Avalonia.Styling
         /// <param name="property">The property.</param>
         /// <param name="value">The property value.</param>
         /// <returns>The selector.</returns>
-        public static Selector PropertyEquals(this Selector previous, AvaloniaProperty property, object value)
+        public static Selector PropertyEquals(this Selector? previous, AvaloniaProperty property, object? value)
         {
-            Contract.Requires<ArgumentNullException>(property != null);
+            _ = property ?? throw new ArgumentNullException(nameof(property));
 
             return new PropertyEqualsSelector(previous, property, value);
         }
diff --git a/src/Avalonia.Styling/Styling/Styles.cs b/src/Avalonia.Styling/Styling/Styles.cs
index c752bdfeb8..81502f1570 100644
--- a/src/Avalonia.Styling/Styling/Styles.cs
+++ b/src/Avalonia.Styling/Styling/Styles.cs
@@ -262,7 +262,7 @@ namespace Avalonia.Styling
             }
         }
 
-        private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void OnCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             static IReadOnlyList<T> ToReadOnlyList<T>(IList list)
             {
@@ -282,7 +282,7 @@ namespace Avalonia.Styling
             {
                 for (var i = 0; i < items.Count; ++i)
                 {
-                    var style = (IStyle)items[i];
+                    var style = (IStyle)items[i]!;
 
                     if (Owner is object && style is IResourceProvider resourceProvider)
                     {
@@ -299,7 +299,7 @@ namespace Avalonia.Styling
             {
                 for (var i = 0; i < items.Count; ++i)
                 {
-                    var style = (IStyle)items[i];
+                    var style = (IStyle)items[i]!;
 
                     if (Owner is object && style is IResourceProvider resourceProvider)
                     {
@@ -315,14 +315,14 @@ namespace Avalonia.Styling
             switch (e.Action)
             {
                 case NotifyCollectionChangedAction.Add:
-                    Add(e.NewItems);
+                    Add(e.NewItems!);
                     break;
                 case NotifyCollectionChangedAction.Remove:
-                    Remove(e.OldItems);
+                    Remove(e.OldItems!);
                     break;
                 case NotifyCollectionChangedAction.Replace:
-                    Remove(e.OldItems);
-                    Add(e.NewItems);
+                    Remove(e.OldItems!);
+                    Add(e.NewItems!);
                     break;
                 case NotifyCollectionChangedAction.Reset:
                     throw new InvalidOperationException("Reset should not be called on Styles.");
diff --git a/src/Avalonia.Styling/Styling/TemplateSelector.cs b/src/Avalonia.Styling/Styling/TemplateSelector.cs
index 5ea8defeda..e8051efa6d 100644
--- a/src/Avalonia.Styling/Styling/TemplateSelector.cs
+++ b/src/Avalonia.Styling/Styling/TemplateSelector.cs
@@ -5,7 +5,7 @@ namespace Avalonia.Styling
     internal class TemplateSelector : Selector
     {
         private readonly Selector _parent;
-        private string _selectorString;
+        private string? _selectorString;
 
         public TemplateSelector(Selector parent)
         {
@@ -24,7 +24,7 @@ namespace Avalonia.Styling
         public override bool IsCombinator => true;
 
         /// <inheritdoc/>
-        public override Type TargetType => null;
+        public override Type? TargetType => null;
 
         public override string ToString()
         {
@@ -48,6 +48,6 @@ namespace Avalonia.Styling
             return _parent.Match(templatedParent, subscribe);
         }
 
-        protected override Selector MovePrevious() => null;
+        protected override Selector? MovePrevious() => null;
     }
 }
diff --git a/src/Avalonia.Themes.Default/Avalonia.Themes.Default.csproj b/src/Avalonia.Themes.Default/Avalonia.Themes.Default.csproj
index d132dc4f5d..678f75b43f 100644
--- a/src/Avalonia.Themes.Default/Avalonia.Themes.Default.csproj
+++ b/src/Avalonia.Themes.Default/Avalonia.Themes.Default.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Markup\Avalonia.Markup.Xaml\Avalonia.Markup.Xaml.csproj" />
diff --git a/src/Avalonia.Themes.Default/CalendarDatePicker.xaml b/src/Avalonia.Themes.Default/CalendarDatePicker.xaml
index 57b77f70ea..3e2e497d2c 100644
--- a/src/Avalonia.Themes.Default/CalendarDatePicker.xaml
+++ b/src/Avalonia.Themes.Default/CalendarDatePicker.xaml
@@ -115,7 +115,11 @@
                  StaysOpen="False">
             <Calendar Name="PART_Calendar"
                       FirstDayOfWeek="{TemplateBinding FirstDayOfWeek}"
-                      IsTodayHighlighted="{TemplateBinding IsTodayHighlighted}"/>
+                      IsTodayHighlighted="{TemplateBinding IsTodayHighlighted}"
+                      SelectedDate="{TemplateBinding SelectedDate, Mode=TwoWay}"
+                      DisplayDate="{TemplateBinding DisplayDate}"
+                      DisplayDateStart="{TemplateBinding DisplayDateStart}"
+                      DisplayDateEnd="{TemplateBinding DisplayDateEnd}" />
           </Popup>
         </Grid>
       </ControlTemplate>
diff --git a/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj b/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj
index f339700b54..885661536c 100644
--- a/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj
+++ b/src/Avalonia.Themes.Fluent/Avalonia.Themes.Fluent.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\Markup\Avalonia.Markup.Xaml\Avalonia.Markup.Xaml.csproj" />
diff --git a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
index 995cca2b82..6c4e94caf1 100644
--- a/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
+++ b/src/Avalonia.Themes.Fluent/Controls/CalendarDatePicker.xaml
@@ -129,7 +129,11 @@
                  IsLightDismissEnabled="True">
             <Calendar Name="PART_Calendar"
                       FirstDayOfWeek="{TemplateBinding FirstDayOfWeek}"
-                      IsTodayHighlighted="{TemplateBinding IsTodayHighlighted}"/>
+                      IsTodayHighlighted="{TemplateBinding IsTodayHighlighted}"
+                      SelectedDate="{TemplateBinding SelectedDate, Mode=TwoWay}"
+                      DisplayDate="{TemplateBinding DisplayDate}"
+                      DisplayDateStart="{TemplateBinding DisplayDateStart}"
+                      DisplayDateEnd="{TemplateBinding DisplayDateEnd}" />
           </Popup>
         </Grid>
       </ControlTemplate>
diff --git a/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs b/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs
index ba7a3868c7..a2c4b0313b 100644
--- a/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs
+++ b/src/Avalonia.Visuals/Animation/Animators/BaseBrushAnimator.cs
@@ -143,7 +143,7 @@ namespace Avalonia.Animation.Animators
                     if (!match(firstKeyType))
                         continue;
 
-                    animator = (IAnimator)Activator.CreateInstance(animatorType);
+                    animator = (IAnimator?)Activator.CreateInstance(animatorType);
                     if (animator != null)
                     {
                         animator.Property = Property;
diff --git a/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs b/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs
index 1b2142f6c9..1d7bfd3748 100644
--- a/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs
+++ b/src/Avalonia.Visuals/Animation/Animators/TransformAnimator.cs
@@ -11,10 +11,10 @@ namespace Avalonia.Animation.Animators
     /// </summary>
     public class TransformAnimator : Animator<double>
     {
-        DoubleAnimator _doubleAnimator;
+        DoubleAnimator? _doubleAnimator;
 
         /// <inheritdoc/>
-        public override IDisposable Apply(Animation animation, Animatable control, IClock clock, IObservable<bool> obsMatch, Action onComplete)
+        public override IDisposable? Apply(Animation animation, Animatable control, IClock clock, IObservable<bool> obsMatch, Action onComplete)
         {
             var ctrl = (Visual)control;
 
diff --git a/src/Avalonia.Visuals/Animation/CompositePageTransition.cs b/src/Avalonia.Visuals/Animation/CompositePageTransition.cs
index 2deebd7792..2a6eae3e38 100644
--- a/src/Avalonia.Visuals/Animation/CompositePageTransition.cs
+++ b/src/Avalonia.Visuals/Animation/CompositePageTransition.cs
@@ -37,7 +37,7 @@ namespace Avalonia.Animation
         public List<IPageTransition> PageTransitions { get; set; } = new List<IPageTransition>();
 
         /// <inheritdoc />
-        public Task Start(Visual from, Visual to, bool forward, CancellationToken cancellationToken)
+        public Task Start(Visual? from, Visual? to, bool forward, CancellationToken cancellationToken)
         {
             var transitionTasks = PageTransitions
                 .Select(transition => transition.Start(from, to, forward, cancellationToken))
diff --git a/src/Avalonia.Visuals/Animation/CrossFade.cs b/src/Avalonia.Visuals/Animation/CrossFade.cs
index 5eaa920b32..608a0880ec 100644
--- a/src/Avalonia.Visuals/Animation/CrossFade.cs
+++ b/src/Avalonia.Visuals/Animation/CrossFade.cs
@@ -100,7 +100,7 @@ namespace Avalonia.Animation
         }
 
         /// <inheritdoc cref="Start(Visual, Visual, CancellationToken)" />
-        public async Task Start(Visual from, Visual to, CancellationToken cancellationToken)
+        public async Task Start(Visual? from, Visual? to, CancellationToken cancellationToken)
         {
             if (cancellationToken.IsCancellationRequested)
             {
@@ -112,7 +112,7 @@ namespace Avalonia.Animation
             {
                 if (to != null)
                 {
-                    disposables.Add(to.SetValue(Visual.OpacityProperty, 0, Data.BindingPriority.Animation));
+                    disposables.Add(to.SetValue(Visual.OpacityProperty, 0, Data.BindingPriority.Animation)!);
                 }
 
                 if (from != null)
@@ -151,7 +151,7 @@ namespace Avalonia.Animation
         /// <returns>
         /// A <see cref="Task"/> that tracks the progress of the animation.
         /// </returns>
-        Task IPageTransition.Start(Visual from, Visual to, bool forward, CancellationToken cancellationToken)
+        Task IPageTransition.Start(Visual? from, Visual? to, bool forward, CancellationToken cancellationToken)
         {
             return Start(from, to, cancellationToken);
         }
diff --git a/src/Avalonia.Visuals/Animation/IPageTransition.cs b/src/Avalonia.Visuals/Animation/IPageTransition.cs
index 2d19ddbb5b..5abfdbbd0d 100644
--- a/src/Avalonia.Visuals/Animation/IPageTransition.cs
+++ b/src/Avalonia.Visuals/Animation/IPageTransition.cs
@@ -26,6 +26,6 @@ namespace Avalonia.Animation
         /// <returns>
         /// A <see cref="Task"/> that tracks the progress of the animation.
         /// </returns>
-        Task Start(Visual from, Visual to, bool forward, CancellationToken cancellationToken);
+        Task Start(Visual? from, Visual? to, bool forward, CancellationToken cancellationToken);
     }
 }
diff --git a/src/Avalonia.Visuals/Animation/PageSlide.cs b/src/Avalonia.Visuals/Animation/PageSlide.cs
index 7d033ccf61..b5a6062593 100644
--- a/src/Avalonia.Visuals/Animation/PageSlide.cs
+++ b/src/Avalonia.Visuals/Animation/PageSlide.cs
@@ -62,7 +62,7 @@ namespace Avalonia.Animation
         public Easing SlideOutEasing { get; set; } = new LinearEasing();
 
         /// <inheritdoc />
-        public async Task Start(Visual from, Visual to, bool forward, CancellationToken cancellationToken)
+        public async Task Start(Visual? from, Visual? to, bool forward, CancellationToken cancellationToken)
         {
             if (cancellationToken.IsCancellationRequested)
             {
@@ -155,17 +155,17 @@ namespace Avalonia.Animation
         /// <remarks>
         /// Any one of the parameters may be null, but not both.
         /// </remarks>
-        private static IVisual GetVisualParent(IVisual from, IVisual to)
+        private static IVisual GetVisualParent(IVisual? from, IVisual? to)
         {
-            var p1 = (from ?? to).VisualParent;
-            var p2 = (to ?? from).VisualParent;
+            var p1 = (from ?? to)!.VisualParent;
+            var p2 = (to ?? from)!.VisualParent;
 
             if (p1 != null && p2 != null && p1 != p2)
             {
                 throw new ArgumentException("Controls for PageSlide must have same parent.");
             }
 
-            return p1;
+            return p1 ?? throw new InvalidOperationException("Cannot determine visual parent.");
         }
     }
 }
diff --git a/src/Avalonia.Visuals/Animation/RenderLoopClock.cs b/src/Avalonia.Visuals/Animation/RenderLoopClock.cs
index 504caef461..de86b5fee2 100644
--- a/src/Avalonia.Visuals/Animation/RenderLoopClock.cs
+++ b/src/Avalonia.Visuals/Animation/RenderLoopClock.cs
@@ -9,7 +9,7 @@ namespace Avalonia.Animation
     {
         protected override void Stop()
         {
-            AvaloniaLocator.Current.GetService<IRenderLoop>().Remove(this);
+            AvaloniaLocator.Current.GetRequiredService<IRenderLoop>().Remove(this);
         }
 
         bool IRenderLoopTask.NeedsUpdate => HasSubscriptions;
diff --git a/src/Avalonia.Visuals/ApiCompatBaseline.txt b/src/Avalonia.Visuals/ApiCompatBaseline.txt
index ee4f70e074..ad9a5fd71a 100644
--- a/src/Avalonia.Visuals/ApiCompatBaseline.txt
+++ b/src/Avalonia.Visuals/ApiCompatBaseline.txt
@@ -5,6 +5,8 @@ InterfacesShouldHaveSameMembers : Interface member 'public System.Threading.Task
 MembersMustExist : Member 'public System.Threading.Tasks.Task Avalonia.Animation.IPageTransition.Start(Avalonia.Visual, Avalonia.Visual, System.Boolean)' does not exist in the implementation but it does exist in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public System.Threading.Tasks.Task Avalonia.Animation.IPageTransition.Start(Avalonia.Visual, Avalonia.Visual, System.Boolean, System.Threading.CancellationToken)' is present in the implementation but not in the contract.
 MembersMustExist : Member 'public System.Threading.Tasks.Task Avalonia.Animation.PageSlide.Start(Avalonia.Visual, Avalonia.Visual, System.Boolean)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'public void Avalonia.Media.GlyphRun..ctor()' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'public void Avalonia.Media.GlyphRun.GlyphTypeface.set(Avalonia.Media.GlyphTypeface)' does not exist in the implementation but it does exist in the contract.
 TypeCannotChangeClassification : Type 'Avalonia.Media.Immutable.ImmutableSolidColorBrush' is a 'class' in the implementation but is a 'struct' in the contract.
 MembersMustExist : Member 'public void Avalonia.Media.TextFormatting.DrawableTextRun.Draw(Avalonia.Media.DrawingContext)' does not exist in the implementation but it does exist in the contract.
 CannotAddAbstractMembers : Member 'public void Avalonia.Media.TextFormatting.DrawableTextRun.Draw(Avalonia.Media.DrawingContext, Avalonia.Point)' is abstract in the implementation but is missing in the contract.
@@ -77,4 +79,4 @@ InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWr
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWriteableBitmapImpl Avalonia.Platform.IPlatformRenderInterface.LoadWriteableBitmap(System.String)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWriteableBitmapImpl Avalonia.Platform.IPlatformRenderInterface.LoadWriteableBitmapToHeight(System.IO.Stream, System.Int32, Avalonia.Visuals.Media.Imaging.BitmapInterpolationMode)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWriteableBitmapImpl Avalonia.Platform.IPlatformRenderInterface.LoadWriteableBitmapToWidth(System.IO.Stream, System.Int32, Avalonia.Visuals.Media.Imaging.BitmapInterpolationMode)' is present in the implementation but not in the contract.
-Total Issues: 78
+Total Issues: 79
diff --git a/src/Avalonia.Visuals/Avalonia.Visuals.csproj b/src/Avalonia.Visuals/Avalonia.Visuals.csproj
index 51ebfcb11f..6c978e970e 100644
--- a/src/Avalonia.Visuals/Avalonia.Visuals.csproj
+++ b/src/Avalonia.Visuals/Avalonia.Visuals.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <RootNamespace>Avalonia</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
@@ -15,4 +15,5 @@
   <Import Project="..\..\build\Rx.props" />
   <Import Project="..\..\build\System.Memory.props" />
   <Import Project="..\..\build\ApiDiff.props" />
+  <Import Project="..\..\build\NullableEnable.props" />
 </Project>
diff --git a/src/Avalonia.Visuals/CornerRadius.cs b/src/Avalonia.Visuals/CornerRadius.cs
index 037bb16e31..893f7c4565 100644
--- a/src/Avalonia.Visuals/CornerRadius.cs
+++ b/src/Avalonia.Visuals/CornerRadius.cs
@@ -91,7 +91,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="obj">The Object to compare against.</param>
         /// <returns>True if the Object is equal to this corner radius; False otherwise.</returns>
-        public override bool Equals(object obj) => obj is CornerRadius other && Equals(other);
+        public override bool Equals(object? obj) => obj is CornerRadius other && Equals(other);
 
         public override int GetHashCode()
         {
diff --git a/src/Avalonia.Visuals/Matrix.cs b/src/Avalonia.Visuals/Matrix.cs
index 243dafe817..b08a0eb98a 100644
--- a/src/Avalonia.Visuals/Matrix.cs
+++ b/src/Avalonia.Visuals/Matrix.cs
@@ -272,7 +272,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="obj">The Object to compare against.</param>
         /// <returns>True if the Object is equal to this matrix; False otherwise.</returns>
-        public override bool Equals(object obj) => obj is Matrix other && Equals(other);
+        public override bool Equals(object? obj) => obj is Matrix other && Equals(other);
 
         /// <summary>
         /// Returns the hash code for this instance.
diff --git a/src/Avalonia.Visuals/Media/BoxShadow.cs b/src/Avalonia.Visuals/Media/BoxShadow.cs
index 50f75365b0..b01f59f5f8 100644
--- a/src/Avalonia.Visuals/Media/BoxShadow.cs
+++ b/src/Avalonia.Visuals/Media/BoxShadow.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Text;
 using Avalonia.Animation.Animators;
@@ -26,7 +27,7 @@ namespace Avalonia.Media
             return OffsetX.Equals(other.OffsetX) && OffsetY.Equals(other.OffsetY) && Blur.Equals(other.Blur) && Spread.Equals(other.Spread) && Color.Equals(other.Color);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is BoxShadow other && Equals(other);
         }
@@ -59,7 +60,7 @@ namespace Avalonia.Media
                 _index = 0;
             }
 
-            public bool TryReadString(out string s)
+            public bool TryReadString([MaybeNullWhen(false)] out string s)
             {
                 s = null;
                 if (_index >= _arr.Length)
@@ -152,11 +153,11 @@ namespace Avalonia.Media
             tokenizer.TryReadString(out var token5);
 
             if (token4 != null) 
-                blur = double.Parse(token3, CultureInfo.InvariantCulture);
+                blur = double.Parse(token3!, CultureInfo.InvariantCulture);
             if (token5 != null)
-                spread = double.Parse(token4, CultureInfo.InvariantCulture);
+                spread = double.Parse(token4!, CultureInfo.InvariantCulture);
 
-            var color = Color.Parse(token5 ?? token4 ?? token3);
+            var color = Color.Parse(token5 ?? token4 ?? token3!);
             return new BoxShadow
             {
                 IsInset = inset,
diff --git a/src/Avalonia.Visuals/Media/BoxShadows.cs b/src/Avalonia.Visuals/Media/BoxShadows.cs
index 810ac70b99..4614ea4e3c 100644
--- a/src/Avalonia.Visuals/Media/BoxShadows.cs
+++ b/src/Avalonia.Visuals/Media/BoxShadows.cs
@@ -8,7 +8,7 @@ namespace Avalonia.Media
     public struct BoxShadows
     {
         private readonly BoxShadow _first;
-        private readonly BoxShadow[] _list;
+        private readonly BoxShadow[]? _list;
         public int Count { get; }
 
         static BoxShadows()
@@ -39,7 +39,7 @@ namespace Avalonia.Media
                     throw new IndexOutOfRangeException();
                 if (c == 0)
                     return _first;
-                return _list[c - 1];
+                return _list![c - 1];
             }
         }
 
@@ -134,7 +134,7 @@ namespace Avalonia.Media
             return true;
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is BoxShadows other && Equals(other);
         }
diff --git a/src/Avalonia.Visuals/Media/Brush.cs b/src/Avalonia.Visuals/Media/Brush.cs
index cf7f5f531c..11fbe9393a 100644
--- a/src/Avalonia.Visuals/Media/Brush.cs
+++ b/src/Avalonia.Visuals/Media/Brush.cs
@@ -19,7 +19,7 @@ namespace Avalonia.Media
             AvaloniaProperty.Register<Brush, double>(nameof(Opacity), 1.0);
 
         /// <inheritdoc/>
-        public event EventHandler Invalidated;
+        public event EventHandler? Invalidated;
 
         static Brush()
         {
@@ -43,18 +43,20 @@ namespace Avalonia.Media
         /// <returns>The <see cref="Color"/>.</returns>
         public static IBrush Parse(string s)
         {
-            Contract.Requires<ArgumentNullException>(s != null);
-            Contract.Requires<FormatException>(s.Length > 0);
+            _ = s ?? throw new ArgumentNullException(nameof(s));
 
-            if (s[0] == '#')
+            if (s.Length > 0)
             {
-                return new ImmutableSolidColorBrush(Color.Parse(s));
-            }
+                if (s[0] == '#')
+                {
+                    return new ImmutableSolidColorBrush(Color.Parse(s));
+                }
 
-            var brush = KnownColors.GetKnownBrush(s);
-            if (brush != null)
-            {
-                return brush;
+                var brush = KnownColors.GetKnownBrush(s);
+                if (brush != null)
+                {
+                    return brush;
+                }
             }
 
             throw new FormatException($"Invalid brush string: '{s}'.");
diff --git a/src/Avalonia.Visuals/Media/BrushConverter.cs b/src/Avalonia.Visuals/Media/BrushConverter.cs
index b3c105ffc7..c501835c15 100644
--- a/src/Avalonia.Visuals/Media/BrushConverter.cs
+++ b/src/Avalonia.Visuals/Media/BrushConverter.cs
@@ -9,14 +9,14 @@ namespace Avalonia.Media
     /// </summary>
     public class BrushConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
         {
-            return Brush.Parse((string)value);
+            return value is string s ? Brush.Parse(s) : null;
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/Avalonia.Visuals/Media/BrushExtensions.cs b/src/Avalonia.Visuals/Media/BrushExtensions.cs
index 87e698e705..2fc8778a5e 100644
--- a/src/Avalonia.Visuals/Media/BrushExtensions.cs
+++ b/src/Avalonia.Visuals/Media/BrushExtensions.cs
@@ -18,7 +18,7 @@ namespace Avalonia.Media
         /// </returns>
         public static IBrush ToImmutable(this IBrush brush)
         {
-            Contract.Requires<ArgumentNullException>(brush != null);
+            _ = brush ?? throw new ArgumentNullException(nameof(brush));
 
             return (brush as IMutableBrush)?.ToImmutable() ?? brush;
         }
@@ -33,7 +33,7 @@ namespace Avalonia.Media
         /// </returns>
         public static ImmutableDashStyle ToImmutable(this IDashStyle style)
         {
-            Contract.Requires<ArgumentNullException>(style != null);
+            _ = style ?? throw new ArgumentNullException(nameof(style));
 
             return style as ImmutableDashStyle ?? ((DashStyle)style).ToImmutable();
         }
@@ -48,7 +48,7 @@ namespace Avalonia.Media
         /// </returns>
         public static ImmutablePen ToImmutable(this IPen pen)
         {
-            Contract.Requires<ArgumentNullException>(pen != null);
+            _ = pen ?? throw new ArgumentNullException(nameof(pen));
 
             return pen as ImmutablePen ?? ((Pen)pen).ToImmutable();
         }
diff --git a/src/Avalonia.Visuals/Media/CharacterHit.cs b/src/Avalonia.Visuals/Media/CharacterHit.cs
index f018b2d8a9..6bbbff4f5b 100644
--- a/src/Avalonia.Visuals/Media/CharacterHit.cs
+++ b/src/Avalonia.Visuals/Media/CharacterHit.cs
@@ -41,7 +41,7 @@ namespace Avalonia.Media
             return FirstCharacterIndex == other.FirstCharacterIndex && TrailingLength == other.TrailingLength;
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is CharacterHit other && Equals(other);
         }
diff --git a/src/Avalonia.Visuals/Media/Color.cs b/src/Avalonia.Visuals/Media/Color.cs
index a57a962db4..083c15cd13 100644
--- a/src/Avalonia.Visuals/Media/Color.cs
+++ b/src/Avalonia.Visuals/Media/Color.cs
@@ -280,7 +280,7 @@ namespace Avalonia.Media
             return A == other.A && R == other.R && G == other.G && B == other.B;
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is Color other && Equals(other);
         }
diff --git a/src/Avalonia.Visuals/Media/CombinedGeometry.cs b/src/Avalonia.Visuals/Media/CombinedGeometry.cs
index b76c496c4e..8f080d05c7 100644
--- a/src/Avalonia.Visuals/Media/CombinedGeometry.cs
+++ b/src/Avalonia.Visuals/Media/CombinedGeometry.cs
@@ -154,8 +154,7 @@ namespace Avalonia.Media
 
             if (g1 is object && g2 is object)
             {
-                var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>() ??
-                    throw new InvalidOperationException("Unable to locate IPlatformRenderInterface.");
+                var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
                 return factory.CreateCombinedGeometry(GeometryCombineMode, g1, g2);
             }
             else if (GeometryCombineMode == GeometryCombineMode.Intersect)
diff --git a/src/Avalonia.Visuals/Media/DashStyle.cs b/src/Avalonia.Visuals/Media/DashStyle.cs
index acba2d3615..2ec9436ede 100644
--- a/src/Avalonia.Visuals/Media/DashStyle.cs
+++ b/src/Avalonia.Visuals/Media/DashStyle.cs
@@ -133,7 +133,7 @@ namespace Avalonia.Media
             }
         }
 
-        private void DashesChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void DashesChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             Invalidated?.Invoke(this, e);
         }
diff --git a/src/Avalonia.Visuals/Media/DrawingContext.cs b/src/Avalonia.Visuals/Media/DrawingContext.cs
index 8e8b116a04..2fbef8c89f 100644
--- a/src/Avalonia.Visuals/Media/DrawingContext.cs
+++ b/src/Avalonia.Visuals/Media/DrawingContext.cs
@@ -20,9 +20,9 @@ namespace Avalonia.Media
         private static ThreadSafeObjectPool<Stack<TransformContainer>> TransformStackPool { get; } =
             ThreadSafeObjectPool<Stack<TransformContainer>>.Default;
 
-        private Stack<PushedState> _states = StateStackPool.Get();
+        private Stack<PushedState>? _states = StateStackPool.Get();
 
-        private Stack<TransformContainer> _transformContainers = TransformStackPool.Get();
+        private Stack<TransformContainer>? _transformContainers = TransformStackPool.Get();
 
         readonly struct TransformContainer
         {
@@ -80,7 +80,7 @@ namespace Avalonia.Media
         /// <param name="rect">The rect in the output to draw to.</param>
         public void DrawImage(IImage source, Rect rect)
         {
-            Contract.Requires<ArgumentNullException>(source != null);
+            _ = source ?? throw new ArgumentNullException(nameof(source));
 
             DrawImage(source, new Rect(source.Size), rect);
         }
@@ -94,7 +94,7 @@ namespace Avalonia.Media
         /// <param name="bitmapInterpolationMode">The bitmap interpolation mode.</param>
         public void DrawImage(IImage source, Rect sourceRect, Rect destRect, BitmapInterpolationMode bitmapInterpolationMode = default)
         {
-            Contract.Requires<ArgumentNullException>(source != null);
+            _ = source ?? throw new ArgumentNullException(nameof(source));
 
             source.Draw(this, sourceRect, destRect, bitmapInterpolationMode);
         }
@@ -121,7 +121,8 @@ namespace Avalonia.Media
         /// <param name="geometry">The geometry.</param>
         public void DrawGeometry(IBrush brush, IPen pen, Geometry geometry)
         {
-            DrawGeometry(brush, pen, geometry.PlatformImpl);
+            if (geometry.PlatformImpl is not null)
+                DrawGeometry(brush, pen, geometry.PlatformImpl);
         }
 
         /// <summary>
@@ -132,7 +133,7 @@ namespace Avalonia.Media
         /// <param name="geometry">The geometry.</param>
         public void DrawGeometry(IBrush brush, IPen pen, IGeometryImpl geometry)
         {
-            Contract.Requires<ArgumentNullException>(geometry != null);
+            _ = geometry ?? throw new ArgumentNullException(nameof(geometry));
 
             if (brush != null || PenIsVisible(pen))
             {
@@ -157,7 +158,7 @@ namespace Avalonia.Media
         /// The brush and the pen can both be null. If the brush is null, then no fill is performed.
         /// If the pen is null, then no stoke is performed. If both the pen and the brush are null, then the drawing is not visible.
         /// </remarks>
-        public void DrawRectangle(IBrush brush, IPen pen, Rect rect, double radiusX = 0, double radiusY = 0,
+        public void DrawRectangle(IBrush? brush, IPen? pen, Rect rect, double radiusX = 0, double radiusY = 0,
             BoxShadows boxShadows = default)
         {
             if (brush == null && !PenIsVisible(pen))
@@ -201,7 +202,7 @@ namespace Avalonia.Media
         /// The brush and the pen can both be null. If the brush is null, then no fill is performed.
         /// If the pen is null, then no stoke is performed. If both the pen and the brush are null, then the drawing is not visible.
         /// </remarks>
-        public void DrawEllipse(IBrush brush, IPen pen, Point center, double radiusX, double radiusY)
+        public void DrawEllipse(IBrush? brush, IPen? pen, Point center, double radiusX, double radiusY)
         {
             if (brush == null && !PenIsVisible(pen))
             {
@@ -230,7 +231,7 @@ namespace Avalonia.Media
         /// <param name="text">The text.</param>
         public void DrawText(IBrush foreground, Point origin, FormattedText text)
         {
-            Contract.Requires<ArgumentNullException>(text != null);
+            _ = text ?? throw new ArgumentNullException(nameof(text));
 
             if (foreground != null)
             {
@@ -245,7 +246,7 @@ namespace Avalonia.Media
         /// <param name="glyphRun">The glyph run.</param>
         public void DrawGlyphRun(IBrush foreground, GlyphRun glyphRun)
         {
-            Contract.Requires<ArgumentNullException>(glyphRun != null);
+            _ = glyphRun ?? throw new ArgumentNullException(nameof(glyphRun));
 
             if (foreground != null)
             {
@@ -279,11 +280,14 @@ namespace Avalonia.Media
                 Clip,
                 MatrixContainer,
                 GeometryClip,
-                OpacityMask
+                OpacityMask,
             }
 
             public PushedState(DrawingContext context, PushedStateType type, Matrix matrix = default(Matrix))
             {
+                if (context._states is null)
+                    throw new ObjectDisposedException(nameof(DrawingContext));
+
                 _context = context;
                 _type = type;
                 _matrix = matrix;
@@ -295,6 +299,8 @@ namespace Avalonia.Media
             {
                 if (_type == PushedStateType.None)
                     return;
+                if (_context._states is null || _context._transformContainers is null)
+                    throw new ObjectDisposedException(nameof(DrawingContext));
                 if (_context._currentLevel != _level)
                     throw new InvalidOperationException("Wrong Push/Pop state order");
                 _context._currentLevel--;
@@ -343,7 +349,14 @@ namespace Avalonia.Media
         /// <returns>A disposable used to undo the clip geometry.</returns>
         public PushedState PushGeometryClip(Geometry clip)
         {
-            Contract.Requires<ArgumentNullException>(clip != null);
+            _ = clip ?? throw new ArgumentNullException(nameof(clip));
+
+            // HACK: This check was added when nullable annotations pointed out that we're potentially
+            // pushing a null value for the clip here. Ideally we'd return an empty PushedState here but
+            // I don't want to make that change as part of adding nullable annotations.
+            if (clip.PlatformImpl is null)
+                throw new InvalidOperationException("Cannot push empty geometry clip.");
+
             PlatformImpl.PushGeometryClip(clip.PlatformImpl);
             return new PushedState(this, PushedState.PushedStateType.GeometryClip);
         }
@@ -407,6 +420,8 @@ namespace Avalonia.Media
         /// <returns>A disposable used to undo the transformation.</returns>
         public PushedState PushTransformContainer()
         {
+            if (_transformContainers is null)
+                throw new ObjectDisposedException(nameof(DrawingContext));
             _transformContainers.Push(new TransformContainer(CurrentTransform, _currentContainerTransform));
             _currentContainerTransform = CurrentTransform * _currentContainerTransform;
             _currentTransform = Matrix.Identity;
@@ -418,6 +433,8 @@ namespace Avalonia.Media
         /// </summary>
         public void Dispose()
         {
+            if (_states is null || _transformContainers is null)
+                throw new ObjectDisposedException(nameof(DrawingContext));
             while (_states.Count != 0)
                 _states.Peek().Dispose();
             StateStackPool.Return(_states);
@@ -430,7 +447,7 @@ namespace Avalonia.Media
                 PlatformImpl.Dispose();
         }
 
-        private static bool PenIsVisible(IPen pen)
+        private static bool PenIsVisible(IPen? pen)
         {
             return pen?.Brush != null && pen.Thickness > 0;
         }
diff --git a/src/Avalonia.Visuals/Media/DrawingImage.cs b/src/Avalonia.Visuals/Media/DrawingImage.cs
index 6fa8d397a5..488822b693 100644
--- a/src/Avalonia.Visuals/Media/DrawingImage.cs
+++ b/src/Avalonia.Visuals/Media/DrawingImage.cs
@@ -26,7 +26,7 @@ namespace Avalonia.Media
             AvaloniaProperty.Register<DrawingImage, Drawing>(nameof(Drawing));
 
         /// <inheritdoc/>
-        public event EventHandler Invalidated;
+        public event EventHandler? Invalidated;
 
         /// <summary>
         /// Gets or sets the drawing content.
diff --git a/src/Avalonia.Visuals/Media/EllipseGeometry.cs b/src/Avalonia.Visuals/Media/EllipseGeometry.cs
index bae6dc3d8c..8211855324 100644
--- a/src/Avalonia.Visuals/Media/EllipseGeometry.cs
+++ b/src/Avalonia.Visuals/Media/EllipseGeometry.cs
@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Platform;
 
 namespace Avalonia.Media
@@ -95,9 +96,9 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        protected override IGeometryImpl CreateDefiningGeometry()
+        protected override IGeometryImpl? CreateDefiningGeometry()
         {
-            var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
 
             if (Rect != default) return factory.CreateEllipseGeometry(Rect);
             
diff --git a/src/Avalonia.Visuals/Media/ExperimentalAcrylicMaterial.cs b/src/Avalonia.Visuals/Media/ExperimentalAcrylicMaterial.cs
index 6b699acd2e..cdea5f5fa3 100644
--- a/src/Avalonia.Visuals/Media/ExperimentalAcrylicMaterial.cs
+++ b/src/Avalonia.Visuals/Media/ExperimentalAcrylicMaterial.cs
@@ -78,7 +78,7 @@ namespace Avalonia.Media
             AvaloniaProperty.Register<ExperimentalAcrylicMaterial, Color>(nameof(FallbackColor));
 
         /// <inheritdoc/>
-        public event EventHandler Invalidated;
+        public event EventHandler? Invalidated;
 
         /// <summary>
         /// Gets or Sets the BackgroundSource <seealso cref="AcrylicBackgroundSource"/>.
@@ -299,14 +299,14 @@ namespace Avalonia.Media
 
             var lightness = (max + min) / 2.0;
 
-            lightness = 1 - ((1 - lightness) * luminosityOpacity.Value);
+            lightness = 1 - ((1 - lightness) * (luminosityOpacity ?? 1));
 
             lightness = 0.13 + (lightness * 0.74);
 
             var luminosityColor = new Color(255, Trim(lightness), Trim(lightness), Trim(lightness));
 
             var compensationMultiplier = 1 - PlatformTransparencyCompensationLevel;
-            return new Color((byte)(255 * Math.Max(Math.Min(PlatformTransparencyCompensationLevel + (luminosityOpacity.Value * compensationMultiplier), 1.0), 0.0)), luminosityColor.R, luminosityColor.G, luminosityColor.B);
+            return new Color((byte)(255 * Math.Max(Math.Min(PlatformTransparencyCompensationLevel + ((luminosityOpacity ?? 1) * compensationMultiplier), 1.0), 0.0)), luminosityColor.R, luminosityColor.G, luminosityColor.B);
         }
 
         /// <summary>
diff --git a/src/Avalonia.Visuals/Media/FontFallback.cs b/src/Avalonia.Visuals/Media/FontFallback.cs
index 240604c5c1..8943b57b31 100644
--- a/src/Avalonia.Visuals/Media/FontFallback.cs
+++ b/src/Avalonia.Visuals/Media/FontFallback.cs
@@ -8,7 +8,7 @@
         /// <summary>
         /// Get or set the fallback <see cref="FontFamily"/>
         /// </summary>
-        public FontFamily FontFamily { get; set; }
+        public FontFamily FontFamily { get; set; } = FontFamily.Default;
 
         /// <summary>
         /// Get or set the <see cref="UnicodeRange"/> that is covered by the fallback.
diff --git a/src/Avalonia.Visuals/Media/FontFamily.cs b/src/Avalonia.Visuals/Media/FontFamily.cs
index f018733235..c4ebc1e0d4 100644
--- a/src/Avalonia.Visuals/Media/FontFamily.cs
+++ b/src/Avalonia.Visuals/Media/FontFamily.cs
@@ -27,7 +27,7 @@ namespace Avalonia.Media
         /// <param name="baseUri">Specifies the base uri that is used to resolve font family assets.</param>
         /// <param name="name">The name of the <see cref="T:Avalonia.Media.FontFamily" />.</param>
         /// <exception cref="T:System.ArgumentException">Base uri must be an absolute uri.</exception>
-        public FontFamily(Uri baseUri, string name)
+        public FontFamily(Uri? baseUri, string name)
         {
             if (string.IsNullOrEmpty(name))
             {
@@ -77,7 +77,7 @@ namespace Avalonia.Media
         /// The family key.
         /// </value>
         /// <remarks>Key is only used for custom fonts.</remarks>
-        public FontFamilyKey Key { get; }
+        public FontFamilyKey? Key { get; }
 
         /// <summary>
         /// Returns <c>True</c> if this instance is the system's default.
@@ -95,7 +95,7 @@ namespace Avalonia.Media
 
         private struct FontFamilyIdentifier
         {
-            public FontFamilyIdentifier(string name, Uri source)
+            public FontFamilyIdentifier(string name, Uri? source)
             {
                 Name = name;
                 Source = source;
@@ -103,7 +103,7 @@ namespace Avalonia.Media
 
             public string Name { get; }
 
-            public Uri Source { get; }
+            public Uri? Source { get; }
         }
 
         private static FontFamilyIdentifier GetFontFamilyIdentifier(string name)
@@ -152,7 +152,7 @@ namespace Avalonia.Media
         /// <exception cref="ArgumentException">
         /// Specified family is not supported.
         /// </exception>
-        public static FontFamily Parse(string s, Uri baseUri)
+        public static FontFamily Parse(string s, Uri? baseUri)
         {
             if (string.IsNullOrEmpty(s))
             {
@@ -192,12 +192,12 @@ namespace Avalonia.Media
             }
         }
 
-        public static bool operator !=(FontFamily a, FontFamily b)
+        public static bool operator !=(FontFamily? a, FontFamily? b)
         {
             return !(a == b);
         }
 
-        public static bool operator ==(FontFamily a, FontFamily b)
+        public static bool operator ==(FontFamily? a, FontFamily? b)
         {
             if (ReferenceEquals(a, b))
             {
@@ -207,7 +207,7 @@ namespace Avalonia.Media
             return !(a is null) && a.Equals(b);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (ReferenceEquals(this, obj))
             {
diff --git a/src/Avalonia.Visuals/Media/FontManager.cs b/src/Avalonia.Visuals/Media/FontManager.cs
index 33e7bf0200..72c1c8dcac 100644
--- a/src/Avalonia.Visuals/Media/FontManager.cs
+++ b/src/Avalonia.Visuals/Media/FontManager.cs
@@ -16,7 +16,7 @@ namespace Avalonia.Media
         private readonly ConcurrentDictionary<Typeface, GlyphTypeface> _glyphTypefaceCache =
             new ConcurrentDictionary<Typeface, GlyphTypeface>();
         private readonly FontFamily _defaultFontFamily;
-        private readonly IReadOnlyList<FontFallback> _fontFallbacks;
+        private readonly IReadOnlyList<FontFallback>? _fontFallbacks;
 
         public FontManager(IFontManagerImpl platformImpl)
         {
@@ -105,7 +105,7 @@ namespace Avalonia.Media
 
                 if (typeface.FontFamily == _defaultFontFamily)
                 {
-                    return null;
+                   throw new InvalidOperationException($"Could not create glyph typeface for: {typeface.FontFamily.Name}.");
                 }
 
                 typeface = new Typeface(_defaultFontFamily, typeface.Style, typeface.Weight);
@@ -126,7 +126,7 @@ namespace Avalonia.Media
         /// </returns>
         public bool TryMatchCharacter(int codepoint, FontStyle fontStyle,
             FontWeight fontWeight,
-            FontFamily fontFamily, CultureInfo culture, out Typeface typeface)
+            FontFamily? fontFamily, CultureInfo? culture, out Typeface typeface)
         {
             if(_fontFallbacks != null)
             {
diff --git a/src/Avalonia.Visuals/Media/FontManagerOptions.cs b/src/Avalonia.Visuals/Media/FontManagerOptions.cs
index 983fd6eb32..54227dce0f 100644
--- a/src/Avalonia.Visuals/Media/FontManagerOptions.cs
+++ b/src/Avalonia.Visuals/Media/FontManagerOptions.cs
@@ -4,8 +4,8 @@ namespace Avalonia.Media
 {
     public class FontManagerOptions
     {
-        public string DefaultFamilyName { get; set; }
+        public string? DefaultFamilyName { get; set; }
 
-        public IReadOnlyList<FontFallback> FontFallbacks { get; set; }
+        public IReadOnlyList<FontFallback>? FontFallbacks { get; set; }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/Fonts/FamilyNameCollection.cs b/src/Avalonia.Visuals/Media/Fonts/FamilyNameCollection.cs
index 96312a5466..99daaf2143 100644
--- a/src/Avalonia.Visuals/Media/Fonts/FamilyNameCollection.cs
+++ b/src/Avalonia.Visuals/Media/Fonts/FamilyNameCollection.cs
@@ -122,12 +122,12 @@ namespace Avalonia.Media.Fonts
             }
         }
 
-        public static bool operator !=(FamilyNameCollection a, FamilyNameCollection b)
+        public static bool operator !=(FamilyNameCollection? a, FamilyNameCollection? b)
         {
             return !(a == b);
         }
 
-        public static bool operator ==(FamilyNameCollection a, FamilyNameCollection b)
+        public static bool operator ==(FamilyNameCollection? a, FamilyNameCollection? b)
         {
             if (ReferenceEquals(a, b))
             {
@@ -144,7 +144,7 @@ namespace Avalonia.Media.Fonts
         /// <returns>
         ///   <c>true</c> if the specified <see cref="object" /> is equal to this instance; otherwise, <c>false</c>.
         /// </returns>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (!(obj is FamilyNameCollection other))
             {
diff --git a/src/Avalonia.Visuals/Media/Fonts/FontFamilyKey.cs b/src/Avalonia.Visuals/Media/Fonts/FontFamilyKey.cs
index eee24e856d..f607c67fed 100644
--- a/src/Avalonia.Visuals/Media/Fonts/FontFamilyKey.cs
+++ b/src/Avalonia.Visuals/Media/Fonts/FontFamilyKey.cs
@@ -12,7 +12,7 @@ namespace Avalonia.Media.Fonts
         /// </summary>
         /// <param name="source"></param>
         /// <param name="baseUri"></param>
-        public FontFamilyKey(Uri source, Uri baseUri = null)
+        public FontFamilyKey(Uri source, Uri? baseUri = null)
         {
             Source = source ?? throw new ArgumentNullException(nameof(source));
 
@@ -27,7 +27,7 @@ namespace Avalonia.Media.Fonts
         /// <summary>
         /// A base URI to use if <see cref="Source"/> is relative
         /// </summary>
-        public Uri BaseUri { get; }
+        public Uri? BaseUri { get; }
 
         /// <summary>
         /// Returns a hash code for this instance.
@@ -55,12 +55,12 @@ namespace Avalonia.Media.Fonts
             }
         }
 
-        public static bool operator !=(FontFamilyKey a, FontFamilyKey b)
+        public static bool operator !=(FontFamilyKey? a, FontFamilyKey? b)
         {
             return !(a == b);
         }
 
-        public static bool operator ==(FontFamilyKey a, FontFamilyKey b)
+        public static bool operator ==(FontFamilyKey? a, FontFamilyKey? b)
         {
             if (ReferenceEquals(a, b))
             {
@@ -77,7 +77,7 @@ namespace Avalonia.Media.Fonts
         /// <returns>
         ///   <c>true</c> if the specified <see cref="object" /> is equal to this instance; otherwise, <c>false</c>.
         /// </returns>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (!(obj is FontFamilyKey other))
             {
diff --git a/src/Avalonia.Visuals/Media/Fonts/FontFamilyLoader.cs b/src/Avalonia.Visuals/Media/Fonts/FontFamilyLoader.cs
index 02298417a4..a54dad7623 100644
--- a/src/Avalonia.Visuals/Media/Fonts/FontFamilyLoader.cs
+++ b/src/Avalonia.Visuals/Media/Fonts/FontFamilyLoader.cs
@@ -32,8 +32,7 @@ namespace Avalonia.Media.Fonts
         /// <returns></returns>
         private static IEnumerable<Uri> GetFontAssetsBySource(FontFamilyKey fontFamilyKey)
         {
-            var assetLoader = AvaloniaLocator.Current.GetService<IAssetLoader>();
-
+            var assetLoader = AvaloniaLocator.Current.GetRequiredService<IAssetLoader>();
             var availableAssets = assetLoader.GetAssets(fontFamilyKey.Source, fontFamilyKey.BaseUri);
 
             var matchingAssets =
@@ -50,7 +49,7 @@ namespace Avalonia.Media.Fonts
         /// <returns></returns>
         private static IEnumerable<Uri> GetFontAssetsByExpression(FontFamilyKey fontFamilyKey)
         {
-            var assetLoader = AvaloniaLocator.Current.GetService<IAssetLoader>();
+            var assetLoader = AvaloniaLocator.Current.GetRequiredService<IAssetLoader>();
 
             var fileName = GetFileName(fontFamilyKey, out var fileExtension, out var location);
 
@@ -87,7 +86,7 @@ namespace Avalonia.Media.Fonts
             {
                 fileExtension = "." + fontFamilyKey.Source.AbsolutePath.Split('.').LastOrDefault();
 
-                var fileName = fontFamilyKey.Source.LocalPath.Replace(fileExtension, string.Empty).Split('.').LastOrDefault();
+                var fileName = fontFamilyKey.Source.LocalPath.Replace(fileExtension, string.Empty).Split('.').Last();
 
                 location = new Uri(fontFamilyKey.Source.AbsoluteUri.Replace("." + fileName + fileExtension, string.Empty), UriKind.RelativeOrAbsolute);
 
diff --git a/src/Avalonia.Visuals/Media/FormattedText.cs b/src/Avalonia.Visuals/Media/FormattedText.cs
index ddffbe7500..f6129eaf6a 100644
--- a/src/Avalonia.Visuals/Media/FormattedText.cs
+++ b/src/Avalonia.Visuals/Media/FormattedText.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using Avalonia.Platform;
 
@@ -10,11 +11,11 @@ namespace Avalonia.Media
     {
         private readonly IPlatformRenderInterface _platform;
         private Size _constraint = Size.Infinity;
-        private IFormattedTextImpl _platformImpl;
-        private IReadOnlyList<FormattedTextStyleSpan> _spans;
+        private IFormattedTextImpl? _platformImpl;
+        private IReadOnlyList<FormattedTextStyleSpan>? _spans;
         private Typeface _typeface;
         private double _fontSize;
-        private string _text;
+        private string? _text;
         private TextAlignment _textAlignment;
         private TextWrapping _textWrapping;
 
@@ -23,7 +24,7 @@ namespace Avalonia.Media
         /// </summary>
         public FormattedText()
         {
-            _platform = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            _platform = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
         }
 
         /// <summary>
@@ -98,7 +99,7 @@ namespace Avalonia.Media
         /// Gets or sets a collection of spans that describe the formatting of subsections of the
         /// text.
         /// </summary>
-        public IReadOnlyList<FormattedTextStyleSpan> Spans
+        public IReadOnlyList<FormattedTextStyleSpan>? Spans
         {
             get => _spans;
             set => Set(ref _spans, value);
@@ -107,7 +108,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets the text.
         /// </summary>
-        public string Text
+        public string? Text
         {
             get => _text;
             set => Set(ref _text, value);
@@ -141,7 +142,7 @@ namespace Avalonia.Media
                 if (_platformImpl == null)
                 {
                     _platformImpl = _platform.CreateFormattedText(
-                        _text,
+                        _text ?? string.Empty,
                         _typeface,
                         _fontSize,
                         _textAlignment,
diff --git a/src/Avalonia.Visuals/Media/FormattedTextStyleSpan.cs b/src/Avalonia.Visuals/Media/FormattedTextStyleSpan.cs
index 92fdd651c3..fcb631d1eb 100644
--- a/src/Avalonia.Visuals/Media/FormattedTextStyleSpan.cs
+++ b/src/Avalonia.Visuals/Media/FormattedTextStyleSpan.cs
@@ -14,7 +14,7 @@
         public FormattedTextStyleSpan(
             int startIndex,
             int length,
-            IBrush foregroundBrush = null)
+            IBrush? foregroundBrush = null)
         {
             StartIndex = startIndex;
             Length = length;
@@ -34,6 +34,6 @@
         /// <summary>
         /// Gets the span's foreground brush.
         /// </summary>
-        public IBrush ForegroundBrush { get; }
+        public IBrush? ForegroundBrush { get; }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/Geometry.cs b/src/Avalonia.Visuals/Media/Geometry.cs
index ccef6665a9..76c67a5cf4 100644
--- a/src/Avalonia.Visuals/Media/Geometry.cs
+++ b/src/Avalonia.Visuals/Media/Geometry.cs
@@ -11,11 +11,11 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Transform"/> property.
         /// </summary>
-        public static readonly StyledProperty<Transform> TransformProperty =
-            AvaloniaProperty.Register<Geometry, Transform>(nameof(Transform));
+        public static readonly StyledProperty<Transform?> TransformProperty =
+            AvaloniaProperty.Register<Geometry, Transform?>(nameof(Transform));
 
         private bool _isDirty = true;
-        private IGeometryImpl _platformImpl;
+        private IGeometryImpl? _platformImpl;
 
         static Geometry()
         {
@@ -25,7 +25,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Raised when the geometry changes.
         /// </summary>
-        public event EventHandler Changed;
+        public event EventHandler? Changed;
 
         /// <summary>
         /// Gets the geometry's bounding rectangle.
@@ -35,7 +35,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets the platform-specific implementation of the geometry.
         /// </summary>
-        public IGeometryImpl PlatformImpl
+        public IGeometryImpl? PlatformImpl
         {
             get
             {
@@ -60,7 +60,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets a transform to apply to the geometry.
         /// </summary>
-        public Transform Transform
+        public Transform? Transform
         {
             get { return GetValue(TransformProperty); }
             set { SetValue(TransformProperty, value); }
@@ -127,7 +127,7 @@ namespace Avalonia.Media
         /// Creates the platform implementation of the geometry, without the transform applied.
         /// </summary>
         /// <returns></returns>
-        protected abstract IGeometryImpl CreateDefiningGeometry();
+        protected abstract IGeometryImpl? CreateDefiningGeometry();
 
         /// <summary>
         /// Invalidates the platform implementation of the geometry.
@@ -141,8 +141,8 @@ namespace Avalonia.Media
 
         private void TransformChanged(AvaloniaPropertyChangedEventArgs e)
         {
-            var oldValue = (Transform)e.OldValue;
-            var newValue = (Transform)e.NewValue;
+            var oldValue = (Transform?)e.OldValue;
+            var newValue = (Transform?)e.NewValue;
 
             if (oldValue != null)
             {
@@ -157,9 +157,9 @@ namespace Avalonia.Media
             TransformChanged(newValue, EventArgs.Empty);
         }
 
-        private void TransformChanged(object sender, EventArgs e)
+        private void TransformChanged(object? sender, EventArgs e)
         {
-            var transform = ((Transform)sender)?.Value;
+            var transform = ((Transform?)sender)?.Value;
 
             if (_platformImpl is ITransformedGeometryImpl t)
             {
@@ -174,7 +174,7 @@ namespace Avalonia.Media
             }
             else if (_platformImpl != null && transform != null && transform != Matrix.Identity)
             {
-                _platformImpl = PlatformImpl.WithTransform(transform.Value);
+                _platformImpl = _platformImpl.WithTransform(transform.Value);
             }
 
             Changed?.Invoke(this, EventArgs.Empty);
diff --git a/src/Avalonia.Visuals/Media/GeometryGroup.cs b/src/Avalonia.Visuals/Media/GeometryGroup.cs
index 01d4923456..c6b666b2eb 100644
--- a/src/Avalonia.Visuals/Media/GeometryGroup.cs
+++ b/src/Avalonia.Visuals/Media/GeometryGroup.cs
@@ -61,8 +61,7 @@ namespace Avalonia.Media
         {
             if (_children?.Count > 0)
             {
-                var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>() ??
-                    throw new InvalidOperationException("Unable to locate IPlatformRenderInterface.");
+                var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
                 return factory.CreateGeometryGroup(FillRule, _children);
             }
 
diff --git a/src/Avalonia.Visuals/Media/GlyphRun.cs b/src/Avalonia.Visuals/Media/GlyphRun.cs
index 234122f6f5..53b35fb31b 100644
--- a/src/Avalonia.Visuals/Media/GlyphRun.cs
+++ b/src/Avalonia.Visuals/Media/GlyphRun.cs
@@ -14,7 +14,7 @@ namespace Avalonia.Media
         private static readonly IComparer<ushort> s_ascendingComparer = Comparer<ushort>.Default;
         private static readonly IComparer<ushort> s_descendingComparer = new ReverseComparer<ushort>();
 
-        private IGlyphRunImpl _glyphRunImpl;
+        private IGlyphRunImpl? _glyphRunImpl;
         private GlyphTypeface _glyphTypeface;
         private double _fontRenderingEmSize;
         private int _biDiLevel;
@@ -27,14 +27,6 @@ namespace Avalonia.Media
         private ReadOnlySlice<ushort> _glyphClusters;
         private ReadOnlySlice<char> _characters;
 
-        /// <summary>
-        ///     Initializes a new instance of the <see cref="GlyphRun"/> class.
-        /// </summary>
-        public GlyphRun()
-        {
-
-        }
-
         /// <summary>
         ///     Initializes a new instance of the <see cref="GlyphRun"/> class by specifying properties of the class.
         /// </summary>
@@ -56,7 +48,7 @@ namespace Avalonia.Media
             ReadOnlySlice<ushort> glyphClusters = default,
             int biDiLevel = 0)
         {
-            GlyphTypeface = glyphTypeface;
+            _glyphTypeface = glyphTypeface;
 
             FontRenderingEmSize = fontRenderingEmSize;
 
@@ -74,13 +66,9 @@ namespace Avalonia.Media
         }
 
         /// <summary>
-        ///     Gets or sets the <see cref="Media.GlyphTypeface"/> for the <see cref="GlyphRun"/>.
+        ///     Gets the <see cref="Media.GlyphTypeface"/> for the <see cref="GlyphRun"/>.
         /// </summary>
-        public GlyphTypeface GlyphTypeface
-        {
-            get => _glyphTypeface;
-            set => Set(ref _glyphTypeface, value);
-        }
+        public GlyphTypeface GlyphTypeface => _glyphTypeface;
 
         /// <summary>
         ///     Gets or sets the em size used for rendering the <see cref="GlyphRun"/>.
@@ -199,7 +187,7 @@ namespace Avalonia.Media
                     Initialize();
                 }
 
-                return _glyphRunImpl;
+                return _glyphRunImpl!;
             }
         }
 
@@ -639,7 +627,7 @@ namespace Avalonia.Media
                 throw new InvalidOperationException();
             }
 
-            var platformRenderInterface = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var platformRenderInterface = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
 
             _glyphRunImpl = platformRenderInterface.CreateGlyphRun(this);
         }
@@ -651,7 +639,7 @@ namespace Avalonia.Media
 
         private class ReverseComparer<T> : IComparer<T>
         {
-            public int Compare(T x, T y)
+            public int Compare(T? x, T? y)
             {
                 return Comparer<T>.Default.Compare(y, x);
             }
diff --git a/src/Avalonia.Visuals/Media/GlyphTypeface.cs b/src/Avalonia.Visuals/Media/GlyphTypeface.cs
index 2be505b9c0..67dfbb84b6 100644
--- a/src/Avalonia.Visuals/Media/GlyphTypeface.cs
+++ b/src/Avalonia.Visuals/Media/GlyphTypeface.cs
@@ -8,8 +8,8 @@ namespace Avalonia.Media
         public const int InvisibleGlyph = 3;
 
         public GlyphTypeface(Typeface typeface) 
-            : this(FontManager.Current?.PlatformImpl.CreateGlyphTypeface(typeface))
-        { 
+            : this(FontManager.Current.PlatformImpl.CreateGlyphTypeface(typeface)) 
+        {
         }
 
         public GlyphTypeface(IGlyphTypefaceImpl platformImpl)
diff --git a/src/Avalonia.Visuals/Media/GradientBrush.cs b/src/Avalonia.Visuals/Media/GradientBrush.cs
index 5f795d4644..c84413ecbb 100644
--- a/src/Avalonia.Visuals/Media/GradientBrush.cs
+++ b/src/Avalonia.Visuals/Media/GradientBrush.cs
@@ -26,7 +26,7 @@ namespace Avalonia.Media
         public static readonly StyledProperty<GradientStops> GradientStopsProperty =
             AvaloniaProperty.Register<GradientBrush, GradientStops>(nameof(GradientStops));
 
-        private IDisposable _gradientStopsSubscription;
+        private IDisposable? _gradientStopsSubscription;
 
         static GradientBrush()
         {
@@ -64,13 +64,13 @@ namespace Avalonia.Media
         {
             if (e.Sender is GradientBrush brush)
             {
-                var oldValue = (GradientStops)e.OldValue;
-                var newValue = (GradientStops)e.NewValue;
+                var oldValue = (GradientStops?)e.OldValue;
+                var newValue = (GradientStops?)e.NewValue;
 
                 if (oldValue != null)
                 {
                     oldValue.CollectionChanged -= brush.GradientStopsChanged;
-                    brush._gradientStopsSubscription.Dispose();
+                    brush._gradientStopsSubscription?.Dispose();
                 }
 
                 if (newValue != null)
@@ -83,12 +83,12 @@ namespace Avalonia.Media
             }
         }
 
-        private void GradientStopsChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void GradientStopsChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             RaiseInvalidated(EventArgs.Empty);
         }
 
-        private void GradientStopChanged(Tuple<object, PropertyChangedEventArgs> e)
+        private void GradientStopChanged(Tuple<object?, PropertyChangedEventArgs> e)
         {
             RaiseInvalidated(EventArgs.Empty);
         }
diff --git a/src/Avalonia.Visuals/Media/IPen.cs b/src/Avalonia.Visuals/Media/IPen.cs
index 0cdac312cc..1cad9948b4 100644
--- a/src/Avalonia.Visuals/Media/IPen.cs
+++ b/src/Avalonia.Visuals/Media/IPen.cs
@@ -8,12 +8,12 @@
         /// <summary>
         /// Gets the brush used to draw the stroke.
         /// </summary>
-        IBrush Brush { get; }
+        IBrush? Brush { get; }
 
         /// <summary>
         /// Gets the style of dashed lines drawn with a <see cref="Pen"/> object.
         /// </summary>
-        IDashStyle DashStyle { get; }
+        IDashStyle? DashStyle { get; }
 
         /// <summary>
         /// Gets the type of shape to use on both ends of a line.
diff --git a/src/Avalonia.Visuals/Media/Imaging/Bitmap.cs b/src/Avalonia.Visuals/Media/Imaging/Bitmap.cs
index 5a0c57b333..647ce13528 100644
--- a/src/Avalonia.Visuals/Media/Imaging/Bitmap.cs
+++ b/src/Avalonia.Visuals/Media/Imaging/Bitmap.cs
@@ -21,8 +21,7 @@ namespace Avalonia.Media.Imaging
         /// <returns>An instance of the <see cref="Bitmap"/> class.</returns>
         public static Bitmap DecodeToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
         {
-            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
-            return new Bitmap(factory.LoadBitmapToWidth(stream, width, interpolationMode));
+            return new Bitmap(GetFactory().LoadBitmapToWidth(stream, width, interpolationMode));
         }
 
         /// <summary>
@@ -35,8 +34,7 @@ namespace Avalonia.Media.Imaging
         /// <returns>An instance of the <see cref="Bitmap"/> class.</returns>
         public static Bitmap DecodeToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
         {
-            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
-            return new Bitmap(factory.LoadBitmapToHeight(stream, height, interpolationMode));
+            return new Bitmap(GetFactory().LoadBitmapToHeight(stream, height, interpolationMode));
         }
 
         /// <summary>
@@ -47,8 +45,7 @@ namespace Avalonia.Media.Imaging
         /// <returns>An instance of the <see cref="Bitmap"/> class.</returns>
         public Bitmap CreateScaledBitmap(PixelSize destinationSize, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
         {
-            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
-            return new Bitmap(factory.ResizeBitmap(PlatformImpl.Item, destinationSize, interpolationMode));
+            return new Bitmap(GetFactory().ResizeBitmap(PlatformImpl.Item, destinationSize, interpolationMode));
         }
 
         /// <summary>
@@ -57,8 +54,7 @@ namespace Avalonia.Media.Imaging
         /// <param name="fileName">The filename of the bitmap.</param>
         public Bitmap(string fileName)
         {
-            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
-            PlatformImpl = RefCountable.Create(factory.LoadBitmap(fileName));
+            PlatformImpl = RefCountable.Create(GetFactory().LoadBitmap(fileName));
         }
 
         /// <summary>
@@ -67,8 +63,7 @@ namespace Avalonia.Media.Imaging
         /// <param name="stream">The stream to read the bitmap from.</param>
         public Bitmap(Stream stream)
         {
-            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
-            PlatformImpl = RefCountable.Create(factory.LoadBitmap(stream));
+            PlatformImpl = RefCountable.Create(GetFactory().LoadBitmap(stream));
         }
 
         /// <summary>
@@ -106,9 +101,8 @@ namespace Avalonia.Media.Imaging
         [Obsolete("Use overload taking an AlphaFormat.")]
         public Bitmap(PixelFormat format, IntPtr data, PixelSize size, Vector dpi, int stride)
         {
-            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
-
-            PlatformImpl = RefCountable.Create(AvaloniaLocator.Current.GetService<IPlatformRenderInterface>()
+            var ri = GetFactory();
+            PlatformImpl = RefCountable.Create(ri
                 .LoadBitmap(format, ri.DefaultAlphaFormat, data, size, dpi, stride));
         }
 
@@ -123,8 +117,7 @@ namespace Avalonia.Media.Imaging
         /// <param name="stride">The number of bytes per row.</param>
         public Bitmap(PixelFormat format, AlphaFormat alphaFormat, IntPtr data, PixelSize size, Vector dpi, int stride)
         {
-            PlatformImpl = RefCountable.Create(AvaloniaLocator.Current.GetService<IPlatformRenderInterface>()
-                .LoadBitmap(format, alphaFormat, data, size, dpi, stride));
+            PlatformImpl = RefCountable.Create(GetFactory().LoadBitmap(format, alphaFormat, data, size, dpi, stride));
         }
 
         /// <inheritdoc/>
@@ -173,5 +166,10 @@ namespace Avalonia.Media.Imaging
                 destRect,
                 bitmapInterpolationMode);
         }
+
+        private static IPlatformRenderInterface GetFactory()
+        {
+            return AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
+        }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/Imaging/CroppedBitmap.cs b/src/Avalonia.Visuals/Media/Imaging/CroppedBitmap.cs
index 70823e114c..be1f6db561 100644
--- a/src/Avalonia.Visuals/Media/Imaging/CroppedBitmap.cs
+++ b/src/Avalonia.Visuals/Media/Imaging/CroppedBitmap.cs
@@ -11,8 +11,8 @@ namespace Avalonia.Media.Imaging
         /// <summary>
         /// Defines the <see cref="Source"/> property.
         /// </summary>
-        public static readonly StyledProperty<IImage> SourceProperty =
-            AvaloniaProperty.Register<CroppedBitmap, IImage>(nameof(Source));
+        public static readonly StyledProperty<IImage?> SourceProperty =
+            AvaloniaProperty.Register<CroppedBitmap, IImage?>(nameof(Source));
 
         /// <summary>
         /// Defines the <see cref="SourceRect"/> property.
@@ -20,7 +20,7 @@ namespace Avalonia.Media.Imaging
         public static readonly StyledProperty<PixelRect> SourceRectProperty =
             AvaloniaProperty.Register<CroppedBitmap, PixelRect>(nameof(SourceRect));
 
-        public event EventHandler Invalidated;
+        public event EventHandler? Invalidated;
 
         static CroppedBitmap()
         {
@@ -31,7 +31,7 @@ namespace Avalonia.Media.Imaging
         /// <summary>
         /// Gets or sets the source for the bitmap.
         /// </summary>
-        public IImage Source
+        public IImage? Source
         {
             get => GetValue(SourceProperty);
             set => SetValue(SourceProperty, value);
@@ -77,19 +77,19 @@ namespace Avalonia.Media.Imaging
         public Size Size {
             get
             {
-                if (Source == null)
+                if (Source is not IBitmap bmp)
                     return Size.Empty;
                 if (SourceRect.IsEmpty)
                     return Source.Size;
-                return SourceRect.Size.ToSizeWithDpi((Source as IBitmap).Dpi);
+                return SourceRect.Size.ToSizeWithDpi(bmp.Dpi);
             }
         }
 
         public void Draw(DrawingContext context, Rect sourceRect, Rect destRect, BitmapInterpolationMode bitmapInterpolationMode)
         {
-            if (Source == null)
+            if (Source is not IBitmap bmp)
                 return;
-            var topLeft = SourceRect.TopLeft.ToPointWithDpi((Source as IBitmap).Dpi);
+            var topLeft = SourceRect.TopLeft.ToPointWithDpi(bmp.Dpi);
             Source.Draw(context, sourceRect.Translate(new Vector(topLeft.X, topLeft.Y)), destRect, bitmapInterpolationMode);           
         }
     }
diff --git a/src/Avalonia.Visuals/Media/Imaging/RenderTargetBitmap.cs b/src/Avalonia.Visuals/Media/Imaging/RenderTargetBitmap.cs
index 928b188f8c..94a5abd918 100644
--- a/src/Avalonia.Visuals/Media/Imaging/RenderTargetBitmap.cs
+++ b/src/Avalonia.Visuals/Media/Imaging/RenderTargetBitmap.cs
@@ -54,11 +54,11 @@ namespace Avalonia.Media.Imaging
         /// <returns>The platform-specific implementation.</returns>
         private static IRenderTargetBitmapImpl CreateImpl(PixelSize size, Vector dpi)
         {
-            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
             return factory.CreateRenderTargetBitmap(size, dpi);
         }
 
         /// <inheritdoc/>
-        public IDrawingContextImpl CreateDrawingContext(IVisualBrushRenderer vbr) => PlatformImpl.Item.CreateDrawingContext(vbr);
+        public IDrawingContextImpl CreateDrawingContext(IVisualBrushRenderer? vbr) => PlatformImpl.Item.CreateDrawingContext(vbr);
     }
 }
diff --git a/src/Avalonia.Visuals/Media/Imaging/WriteableBitmap.cs b/src/Avalonia.Visuals/Media/Imaging/WriteableBitmap.cs
index b0e1a954e6..40a24db338 100644
--- a/src/Avalonia.Visuals/Media/Imaging/WriteableBitmap.cs
+++ b/src/Avalonia.Visuals/Media/Imaging/WriteableBitmap.cs
@@ -46,7 +46,7 @@ namespace Avalonia.Media.Imaging
 
         public static WriteableBitmap Decode(Stream stream)
         {
-            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var ri = GetFactory();
 
             return new WriteableBitmap(ri.LoadWriteableBitmap(stream));
         }
@@ -61,7 +61,7 @@ namespace Avalonia.Media.Imaging
         /// <returns>An instance of the <see cref="WriteableBitmap"/> class.</returns>
         public new static WriteableBitmap DecodeToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
         {
-            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var ri = GetFactory();
 
             return new WriteableBitmap(ri.LoadWriteableBitmapToWidth(stream, width, interpolationMode));
         }
@@ -76,19 +76,24 @@ namespace Avalonia.Media.Imaging
         /// <returns>An instance of the <see cref="WriteableBitmap"/> class.</returns>
         public new static WriteableBitmap DecodeToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
         {
-            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var ri = GetFactory();
 
             return new WriteableBitmap(ri.LoadWriteableBitmapToHeight(stream, height, interpolationMode));
         }
 
         private static IBitmapImpl CreatePlatformImpl(PixelSize size, in Vector dpi, PixelFormat? format, AlphaFormat? alphaFormat)
         {
-            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var ri = GetFactory();
 
             PixelFormat finalFormat = format ?? ri.DefaultPixelFormat;
             AlphaFormat finalAlphaFormat = alphaFormat ?? ri.DefaultAlphaFormat;
 
             return ri.CreateWriteableBitmap(size, dpi, finalFormat, finalAlphaFormat);
         }
+
+        private static IPlatformRenderInterface GetFactory()
+        {
+            return AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
+        }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/Immutable/ImmutableDashStyle.cs b/src/Avalonia.Visuals/Media/Immutable/ImmutableDashStyle.cs
index 2dd188e0a9..82485c13b0 100644
--- a/src/Avalonia.Visuals/Media/Immutable/ImmutableDashStyle.cs
+++ b/src/Avalonia.Visuals/Media/Immutable/ImmutableDashStyle.cs
@@ -30,10 +30,10 @@ namespace Avalonia.Media.Immutable
         public double Offset { get; }
 
         /// <inheritdoc/>
-        public override bool Equals(object obj) => Equals(obj as IDashStyle);
+        public override bool Equals(object? obj) => Equals(obj as IDashStyle);
 
         /// <inheritdoc/>
-        public bool Equals(IDashStyle other)
+        public bool Equals(IDashStyle? other)
         {
             if (ReferenceEquals(this, other))
             {
diff --git a/src/Avalonia.Visuals/Media/Immutable/ImmutablePen.cs b/src/Avalonia.Visuals/Media/Immutable/ImmutablePen.cs
index 3256f4b11a..8a53eaf7b8 100644
--- a/src/Avalonia.Visuals/Media/Immutable/ImmutablePen.cs
+++ b/src/Avalonia.Visuals/Media/Immutable/ImmutablePen.cs
@@ -21,7 +21,7 @@ namespace Avalonia.Media.Immutable
         public ImmutablePen(
             uint color,
             double thickness = 1.0,
-            ImmutableDashStyle dashStyle = null,
+            ImmutableDashStyle? dashStyle = null,
             PenLineCap lineCap = PenLineCap.Flat,
             PenLineJoin lineJoin = PenLineJoin.Miter,
             double miterLimit = 10.0) : this(new ImmutableSolidColorBrush(color), thickness, dashStyle, lineCap, lineJoin, miterLimit)
@@ -38,9 +38,9 @@ namespace Avalonia.Media.Immutable
         /// <param name="lineJoin">The line join.</param>
         /// <param name="miterLimit">The miter limit.</param>
         public ImmutablePen(
-            IBrush brush,
+            IBrush? brush,
             double thickness = 1.0,
-            ImmutableDashStyle dashStyle = null,
+            ImmutableDashStyle? dashStyle = null,
             PenLineCap lineCap = PenLineCap.Flat,
             PenLineJoin lineJoin = PenLineJoin.Miter,
             double miterLimit = 10.0)
@@ -58,7 +58,7 @@ namespace Avalonia.Media.Immutable
         /// <summary>
         /// Gets the brush used to draw the stroke.
         /// </summary>
-        public IBrush Brush { get; }
+        public IBrush? Brush { get; }
 
         /// <summary>
         /// Gets the stroke thickness.
@@ -68,7 +68,7 @@ namespace Avalonia.Media.Immutable
         /// <summary>
         /// Specifies the style of dashed lines drawn with a <see cref="Pen"/> object.
         /// </summary>
-        public IDashStyle DashStyle { get; }
+        public IDashStyle? DashStyle { get; }
 
         /// <summary>
         /// Specifies the type of graphic shape to use on both ends of a line.
@@ -87,10 +87,10 @@ namespace Avalonia.Media.Immutable
         public double MiterLimit { get; }
 
         /// <inheritdoc/>
-        public override bool Equals(object obj) => Equals(obj as IPen);
+        public override bool Equals(object? obj) => Equals(obj as IPen);
 
         /// <inheritdoc/>
-        public bool Equals(IPen other)
+        public bool Equals(IPen? other)
         {
             if (ReferenceEquals(this, other))
             {
diff --git a/src/Avalonia.Visuals/Media/Immutable/ImmutableSolidColorBrush.cs b/src/Avalonia.Visuals/Media/Immutable/ImmutableSolidColorBrush.cs
index 8e93ac580e..46e1df4054 100644
--- a/src/Avalonia.Visuals/Media/Immutable/ImmutableSolidColorBrush.cs
+++ b/src/Avalonia.Visuals/Media/Immutable/ImmutableSolidColorBrush.cs
@@ -46,14 +46,14 @@ namespace Avalonia.Media.Immutable
         /// </summary>
         public double Opacity { get; }
 
-        public bool Equals(ImmutableSolidColorBrush other)
+        public bool Equals(ImmutableSolidColorBrush? other)
         {
             if (ReferenceEquals(null, other)) return false;
             if (ReferenceEquals(this, other)) return true;
             return Color.Equals(other.Color) && Opacity.Equals(other.Opacity);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is ImmutableSolidColorBrush other && Equals(other);
         }
diff --git a/src/Avalonia.Visuals/Media/ImmutableExperimentalAcrylicMaterial.cs b/src/Avalonia.Visuals/Media/ImmutableExperimentalAcrylicMaterial.cs
index f46d76cf3f..f8487243de 100644
--- a/src/Avalonia.Visuals/Media/ImmutableExperimentalAcrylicMaterial.cs
+++ b/src/Avalonia.Visuals/Media/ImmutableExperimentalAcrylicMaterial.cs
@@ -34,7 +34,7 @@ namespace Avalonia.Media
 
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is ImmutableExperimentalAcrylicMaterial other && Equals(other);
         }
diff --git a/src/Avalonia.Visuals/Media/KnownColors.cs b/src/Avalonia.Visuals/Media/KnownColors.cs
index fe09f5f538..8f07b5f8ac 100644
--- a/src/Avalonia.Visuals/Media/KnownColors.cs
+++ b/src/Avalonia.Visuals/Media/KnownColors.cs
@@ -20,7 +20,7 @@ namespace Avalonia.Media
             foreach (var field in typeof(KnownColor).GetRuntimeFields())
             {
                 if (field.FieldType != typeof(KnownColor)) continue;
-                var knownColor = (KnownColor)field.GetValue(null);
+                var knownColor = (KnownColor)field.GetValue(null)!;
                 if (knownColor == KnownColor.None) continue;
 
                 knownColorNames.Add(field.Name, knownColor);
@@ -41,7 +41,7 @@ namespace Avalonia.Media
         }
 
 #if !BUILDTASK
-        public static ISolidColorBrush GetKnownBrush(string s)
+        public static ISolidColorBrush? GetKnownBrush(string s)
         {
             var color = GetKnownColor(s);
             return color != KnownColor.None ? color.ToBrush() : null;
@@ -58,7 +58,7 @@ namespace Avalonia.Media
             return KnownColor.None;
         }
 
-        public static string GetKnownColorName(uint rgb)
+        public static string? GetKnownColorName(uint rgb)
         {
             return _knownColors.TryGetValue(rgb, out var name) ? name : null;
         }
@@ -230,4 +230,4 @@ namespace Avalonia.Media
         Yellow = 0xffffff00,
         YellowGreen = 0xff9acd32
     }
-}
\ No newline at end of file
+}
diff --git a/src/Avalonia.Visuals/Media/LineGeometry.cs b/src/Avalonia.Visuals/Media/LineGeometry.cs
index 94b638114b..6ac92ea33b 100644
--- a/src/Avalonia.Visuals/Media/LineGeometry.cs
+++ b/src/Avalonia.Visuals/Media/LineGeometry.cs
@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Platform;
 
 namespace Avalonia.Media
@@ -67,9 +68,9 @@ namespace Avalonia.Media
         }
 
         /// <inheritdoc/>
-        protected override IGeometryImpl CreateDefiningGeometry()
+        protected override IGeometryImpl? CreateDefiningGeometry()
         {
-            var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
 
             return factory.CreateLineGeometry(StartPoint, EndPoint);
         }
diff --git a/src/Avalonia.Visuals/Media/MaterialExtensions.cs b/src/Avalonia.Visuals/Media/MaterialExtensions.cs
index c0b445c357..0b3d86d0a4 100644
--- a/src/Avalonia.Visuals/Media/MaterialExtensions.cs
+++ b/src/Avalonia.Visuals/Media/MaterialExtensions.cs
@@ -14,7 +14,7 @@ namespace Avalonia.Media
         /// </returns>
         public static IExperimentalAcrylicMaterial ToImmutable(this IExperimentalAcrylicMaterial material)
         {
-            Contract.Requires<ArgumentNullException>(material != null);
+            _ = material ?? throw new ArgumentNullException(nameof(material));
 
             return (material as IMutableExperimentalAcrylicMaterial)?.ToImmutable() ?? material;
         }
diff --git a/src/Avalonia.Visuals/Media/PathGeometry.cs b/src/Avalonia.Visuals/Media/PathGeometry.cs
index 3d11c19b7d..2c8a51c541 100644
--- a/src/Avalonia.Visuals/Media/PathGeometry.cs
+++ b/src/Avalonia.Visuals/Media/PathGeometry.cs
@@ -11,8 +11,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Figures"/> property.
         /// </summary>
-        public static readonly DirectProperty<PathGeometry, PathFigures> FiguresProperty =
-            AvaloniaProperty.RegisterDirect<PathGeometry, PathFigures>(nameof(Figures), g => g.Figures, (g, f) => g.Figures = f);
+        public static readonly DirectProperty<PathGeometry, PathFigures?> FiguresProperty =
+            AvaloniaProperty.RegisterDirect<PathGeometry, PathFigures?>(nameof(Figures), g => g.Figures, (g, f) => g.Figures = f);
 
         /// <summary>
         /// Defines the <see cref="FillRule"/> property.
@@ -20,9 +20,9 @@ namespace Avalonia.Media
         public static readonly StyledProperty<FillRule> FillRuleProperty =
                                  AvaloniaProperty.Register<PathGeometry, FillRule>(nameof(FillRule));
 
-        private PathFigures _figures;
-        private IDisposable _figuresObserver;
-        private IDisposable _figuresPropertiesObserver;
+        private PathFigures? _figures;
+        private IDisposable? _figuresObserver;
+        private IDisposable? _figuresPropertiesObserver;
 
         static PathGeometry()
         {
@@ -35,7 +35,7 @@ namespace Avalonia.Media
         /// </summary>
         public PathGeometry()
         {
-            Figures = new PathFigures();
+            _figures = new PathFigures();
         }
 
         /// <summary>
@@ -63,7 +63,7 @@ namespace Avalonia.Media
         /// The figures.
         /// </value>
         [Content]
-        public PathFigures Figures
+        public PathFigures? Figures
         {
             get { return _figures; }
             set { SetAndRaise(FiguresProperty, ref _figures, value); }
@@ -81,15 +81,20 @@ namespace Avalonia.Media
             set { SetValue(FillRuleProperty, value); }
         }
 
-        protected override IGeometryImpl CreateDefiningGeometry()
+        protected override IGeometryImpl? CreateDefiningGeometry()
         {
-            var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var figures = Figures;
+
+            if (figures is null)
+                return null;
+
+            var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
             var geometry = factory.CreateStreamGeometry();
 
             using (var ctx = new StreamGeometryContext(geometry.Open()))
             {
                 ctx.SetFillRule(FillRule);
-                foreach (var f in Figures)
+                foreach (var f in figures)
                 {
                     f.ApplyTo(ctx);
                 }
@@ -98,7 +103,7 @@ namespace Avalonia.Media
             return geometry;
         }
 
-        private void OnFiguresChanged(PathFigures figures)
+        private void OnFiguresChanged(PathFigures? figures)
         {
             _figuresObserver?.Dispose();
             _figuresPropertiesObserver?.Dispose();
@@ -120,12 +125,15 @@ namespace Avalonia.Media
  
         }
 
-        private void InvalidateGeometryFromSegments(object _, EventArgs __)
+        private void InvalidateGeometryFromSegments(object? _, EventArgs __)
         {
             InvalidateGeometry();
         }
 
         public override string ToString()
-            => $"{(FillRule != FillRule.EvenOdd ? "F1 " : "")}{(string.Join(" ", Figures))}";
+        {
+            var figuresString = _figures is not null ? string.Join(" ", _figures) : string.Empty;
+            return $"{(FillRule != FillRule.EvenOdd ? "F1 " : "")}{figuresString}";
+        }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/PathGeometryCollections.cs b/src/Avalonia.Visuals/Media/PathGeometryCollections.cs
index 1589d2f5be..1165b192a7 100644
--- a/src/Avalonia.Visuals/Media/PathGeometryCollections.cs
+++ b/src/Avalonia.Visuals/Media/PathGeometryCollections.cs
@@ -20,11 +20,11 @@ namespace Avalonia.Media
                 parser.Parse(pathData);
             }
 
-            return pathGeometry.Figures;
+            return pathGeometry.Figures!;
         }
     }
 
     public sealed class PathSegments : AvaloniaList<PathSegment>
     {
     }
-}
\ No newline at end of file
+}
diff --git a/src/Avalonia.Visuals/Media/PathMarkupParser.cs b/src/Avalonia.Visuals/Media/PathMarkupParser.cs
index 8b9d0833db..30c5206125 100644
--- a/src/Avalonia.Visuals/Media/PathMarkupParser.cs
+++ b/src/Avalonia.Visuals/Media/PathMarkupParser.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.IO;
 using Avalonia.Platform;
@@ -27,7 +28,7 @@ namespace Avalonia.Media
                     { 'Z', Command.Close },
                 };
 
-        private IGeometryContext _geometryContext;
+        private IGeometryContext? _geometryContext;
         private Point _currentPoint;
         private Point? _beginFigurePoint;
         private Point? _previousControlPoint;
@@ -98,6 +99,8 @@ namespace Avalonia.Media
         /// <param name="pathData">The path data.</param>
         public void Parse(string pathData)
         {
+            ThrowIfDisposed();
+
             var span = pathData.AsSpan();
             _currentPoint = new Point();
 
@@ -171,6 +174,8 @@ namespace Avalonia.Media
 
         private void CreateFigure()
         {
+            ThrowIfDisposed();
+
             if (_isOpen)
             {
                 _geometryContext.EndFigure(false);
@@ -185,6 +190,8 @@ namespace Avalonia.Media
 
         private void SetFillRule(ref ReadOnlySpan<char> span)
         {
+            ThrowIfDisposed();
+
             if (!ReadArgument(ref span, out var fillRule) || fillRule.Length != 1)
             {
                 throw new InvalidDataException("Invalid fill rule.");
@@ -209,6 +216,8 @@ namespace Avalonia.Media
 
         private void CloseFigure()
         {
+            ThrowIfDisposed();
+
             if (_isOpen)
             {
                 _geometryContext.EndFigure(true);
@@ -244,6 +253,8 @@ namespace Avalonia.Media
 
         private void AddLine(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             _currentPoint = relative
                                 ? ReadRelativePoint(ref span, _currentPoint)
                                 : ReadPoint(ref span);
@@ -258,6 +269,8 @@ namespace Avalonia.Media
 
         private void AddHorizontalLine(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             _currentPoint = relative
                                 ? new Point(_currentPoint.X + ReadDouble(ref span), _currentPoint.Y)
                                 : _currentPoint.WithX(ReadDouble(ref span));
@@ -272,6 +285,8 @@ namespace Avalonia.Media
 
         private void AddVerticalLine(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             _currentPoint = relative
                                 ? new Point(_currentPoint.X, _currentPoint.Y + ReadDouble(ref span))
                                 : _currentPoint.WithY(ReadDouble(ref span));
@@ -286,6 +301,8 @@ namespace Avalonia.Media
 
         private void AddCubicBezierCurve(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             var point1 = relative
                     ? ReadRelativePoint(ref span, _currentPoint)
                     : ReadPoint(ref span);
@@ -316,6 +333,8 @@ namespace Avalonia.Media
 
         private void AddQuadraticBezierCurve(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             var start = relative
                     ? ReadRelativePoint(ref span, _currentPoint)
                     : ReadPoint(ref span);
@@ -340,6 +359,8 @@ namespace Avalonia.Media
 
         private void AddSmoothCubicBezierCurve(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             var point2 = relative
                     ? ReadRelativePoint(ref span, _currentPoint)
                     : ReadPoint(ref span);
@@ -369,6 +390,8 @@ namespace Avalonia.Media
 
         private void AddSmoothQuadraticBezierCurve(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             var end = relative
                     ? ReadRelativePoint(ref span, _currentPoint)
                     : ReadPoint(ref span);
@@ -390,6 +413,8 @@ namespace Avalonia.Media
 
         private void AddArc(ref ReadOnlySpan<char> span, bool relative)
         {
+            ThrowIfDisposed();
+
             var size = ReadSize(ref span);
 
             span = ReadSeparator(span);
@@ -570,5 +595,12 @@ namespace Avalonia.Media
             span = span.Slice(1);
             return true;
         }
+
+        [MemberNotNull(nameof(_geometryContext))]
+        private void ThrowIfDisposed()
+        {
+            if (_isDisposed || _geometryContext is null)
+                throw new ObjectDisposedException(nameof(PathMarkupParser));
+        }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/Pen.cs b/src/Avalonia.Visuals/Media/Pen.cs
index eb44b3f21e..7c966a35cf 100644
--- a/src/Avalonia.Visuals/Media/Pen.cs
+++ b/src/Avalonia.Visuals/Media/Pen.cs
@@ -12,8 +12,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="Brush"/> property.
         /// </summary>
-        public static readonly StyledProperty<IBrush> BrushProperty =
-            AvaloniaProperty.Register<Pen, IBrush>(nameof(Brush));
+        public static readonly StyledProperty<IBrush?> BrushProperty =
+            AvaloniaProperty.Register<Pen, IBrush?>(nameof(Brush));
 
         /// <summary>
         /// Defines the <see cref="Thickness"/> property.
@@ -24,8 +24,8 @@ namespace Avalonia.Media
         /// <summary>
         /// Defines the <see cref="DashStyle"/> property.
         /// </summary>
-        public static readonly StyledProperty<IDashStyle> DashStyleProperty =
-            AvaloniaProperty.Register<Pen, IDashStyle>(nameof(DashStyle));
+        public static readonly StyledProperty<IDashStyle?> DashStyleProperty =
+            AvaloniaProperty.Register<Pen, IDashStyle?>(nameof(DashStyle));
 
         /// <summary>
         /// Defines the <see cref="LineCap"/> property.
@@ -64,7 +64,7 @@ namespace Avalonia.Media
         public Pen(
             uint color,
             double thickness = 1.0,
-            IDashStyle dashStyle = null,
+            IDashStyle? dashStyle = null,
             PenLineCap lineCap = PenLineCap.Flat,
             PenLineJoin lineJoin = PenLineJoin.Miter,
             double miterLimit = 10.0) : this(new SolidColorBrush(color), thickness, dashStyle, lineCap, lineJoin, miterLimit)
@@ -81,9 +81,9 @@ namespace Avalonia.Media
         /// <param name="lineJoin">The line join.</param>
         /// <param name="miterLimit">The miter limit.</param>
         public Pen(
-            IBrush brush,
+            IBrush? brush,
             double thickness = 1.0,
-            IDashStyle dashStyle = null,
+            IDashStyle? dashStyle = null,
             PenLineCap lineCap = PenLineCap.Flat,
             PenLineJoin lineJoin = PenLineJoin.Miter,
             double miterLimit = 10.0)
@@ -110,7 +110,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets the brush used to draw the stroke.
         /// </summary>
-        public IBrush Brush
+        public IBrush? Brush
         {
             get => GetValue(BrushProperty);
             set => SetValue(BrushProperty, value);
@@ -128,7 +128,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets or sets the style of dashed lines drawn with a <see cref="Pen"/> object.
         /// </summary>
-        public IDashStyle DashStyle
+        public IDashStyle? DashStyle
         {
             get => GetValue(DashStyleProperty);
             set => SetValue(DashStyleProperty, value);
@@ -165,7 +165,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Raised when the pen changes.
         /// </summary>
-        public event EventHandler Invalidated;
+        public event EventHandler? Invalidated;
 
         /// <summary>
         /// Creates an immutable clone of the brush.
@@ -244,6 +244,6 @@ namespace Avalonia.Media
         /// <param name="e">The event args.</param>
         protected void RaiseInvalidated(EventArgs e) => Invalidated?.Invoke(this, e);
 
-        private void AffectsRenderInvalidated(object sender, EventArgs e) => RaiseInvalidated(EventArgs.Empty);
+        private void AffectsRenderInvalidated(object? sender, EventArgs e) => RaiseInvalidated(EventArgs.Empty);
     }
 }
diff --git a/src/Avalonia.Visuals/Media/PixelPoint.cs b/src/Avalonia.Visuals/Media/PixelPoint.cs
index 7d62d7bc23..502eb205a6 100644
--- a/src/Avalonia.Visuals/Media/PixelPoint.cs
+++ b/src/Avalonia.Visuals/Media/PixelPoint.cs
@@ -144,7 +144,7 @@ namespace Avalonia
         /// <returns>
         /// True if <paramref name="obj"/> is a point that equals the current point.
         /// </returns>
-        public override bool Equals(object obj) => obj is PixelPoint other && Equals(other);
+        public override bool Equals(object? obj) => obj is PixelPoint other && Equals(other);
 
         /// <summary>
         /// Returns a hash code for a <see cref="PixelPoint"/>.
diff --git a/src/Avalonia.Visuals/Media/PixelRect.cs b/src/Avalonia.Visuals/Media/PixelRect.cs
index 32a728475f..0059a4b483 100644
--- a/src/Avalonia.Visuals/Media/PixelRect.cs
+++ b/src/Avalonia.Visuals/Media/PixelRect.cs
@@ -208,7 +208,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="obj">The object to compare against.</param>
         /// <returns>True if the object is equal to this rectangle; false otherwise.</returns>
-        public override bool Equals(object obj) => obj is PixelRect other && Equals(other);
+        public override bool Equals(object? obj) => obj is PixelRect other && Equals(other);
 
         /// <summary>
         /// Returns the hash code for this instance.
diff --git a/src/Avalonia.Visuals/Media/PixelSize.cs b/src/Avalonia.Visuals/Media/PixelSize.cs
index 530b01ed90..5a34c6f6b5 100644
--- a/src/Avalonia.Visuals/Media/PixelSize.cs
+++ b/src/Avalonia.Visuals/Media/PixelSize.cs
@@ -94,7 +94,7 @@ namespace Avalonia
         /// <returns>
         /// True if <paramref name="obj"/> is a size that equals the current size.
         /// </returns>
-        public override bool Equals(object obj) => obj is PixelSize other && Equals(other);
+        public override bool Equals(object? obj) => obj is PixelSize other && Equals(other);
 
         /// <summary>
         /// Returns a hash code for a <see cref="PixelSize"/>.
diff --git a/src/Avalonia.Visuals/Media/PixelVector.cs b/src/Avalonia.Visuals/Media/PixelVector.cs
index f32e9c0178..79e7b94c21 100644
--- a/src/Avalonia.Visuals/Media/PixelVector.cs
+++ b/src/Avalonia.Visuals/Media/PixelVector.cs
@@ -143,7 +143,7 @@ namespace Avalonia
             return Math.Abs(_x - other._x) < tolerance && Math.Abs(_y - other._y) < tolerance;
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (ReferenceEquals(null, obj)) return false;
 
diff --git a/src/Avalonia.Visuals/Media/PolylineGeometry.cs b/src/Avalonia.Visuals/Media/PolylineGeometry.cs
index 94c809d432..dd3c298b5b 100644
--- a/src/Avalonia.Visuals/Media/PolylineGeometry.cs
+++ b/src/Avalonia.Visuals/Media/PolylineGeometry.cs
@@ -24,7 +24,7 @@ namespace Avalonia.Media
             AvaloniaProperty.Register<PolylineGeometry, bool>(nameof(IsFilled));
 
         private Points _points;
-        private IDisposable _pointsObserver;
+        private IDisposable? _pointsObserver;
 
         static PolylineGeometry()
         {
@@ -37,7 +37,7 @@ namespace Avalonia.Media
         /// </summary>
         public PolylineGeometry()
         {
-            Points = new Points();
+            _points = new Points();
         }
 
         /// <summary>
@@ -74,9 +74,9 @@ namespace Avalonia.Media
             return new PolylineGeometry(Points, IsFilled);
         }
 
-        protected override IGeometryImpl CreateDefiningGeometry()
+        protected override IGeometryImpl? CreateDefiningGeometry()
         {
-            var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
             var geometry = factory.CreateStreamGeometry();
 
             using (var context = geometry.Open())
@@ -97,7 +97,7 @@ namespace Avalonia.Media
             return geometry;
         }
 
-        private void OnPointsChanged(Points newValue)
+        private void OnPointsChanged(Points? newValue)
         {
             _pointsObserver?.Dispose();
             _pointsObserver = newValue?.ForEachItem(
diff --git a/src/Avalonia.Visuals/Media/RectangleGeometry.cs b/src/Avalonia.Visuals/Media/RectangleGeometry.cs
index 743e103a88..0bf9eb5664 100644
--- a/src/Avalonia.Visuals/Media/RectangleGeometry.cs
+++ b/src/Avalonia.Visuals/Media/RectangleGeometry.cs
@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Platform;
 
 namespace Avalonia.Media
@@ -46,9 +47,9 @@ namespace Avalonia.Media
         /// <inheritdoc/>
         public override Geometry Clone() => new RectangleGeometry(Rect);
 
-        protected override IGeometryImpl CreateDefiningGeometry()
+        protected override IGeometryImpl? CreateDefiningGeometry()
         {
-            var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
 
             return factory.CreateRectangleGeometry(Rect);
         }
diff --git a/src/Avalonia.Visuals/Media/StreamGeometry.cs b/src/Avalonia.Visuals/Media/StreamGeometry.cs
index be914cc7b2..fb79488e0f 100644
--- a/src/Avalonia.Visuals/Media/StreamGeometry.cs
+++ b/src/Avalonia.Visuals/Media/StreamGeometry.cs
@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Platform;
 
 namespace Avalonia.Media
@@ -7,7 +8,7 @@ namespace Avalonia.Media
     /// </summary>
     public class StreamGeometry : Geometry
     {
-        IStreamGeometryImpl _impl;
+        IStreamGeometryImpl? _impl;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StreamGeometry"/> class.
@@ -46,7 +47,7 @@ namespace Avalonia.Media
         /// <inheritdoc/>
         public override Geometry Clone()
         {
-            return new StreamGeometry(((IStreamGeometryImpl)PlatformImpl).Clone());
+            return new StreamGeometry(((IStreamGeometryImpl)PlatformImpl!).Clone());
         }
 
         /// <summary>
@@ -57,15 +58,15 @@ namespace Avalonia.Media
         /// </returns>
         public StreamGeometryContext Open()
         {
-            return new StreamGeometryContext(((IStreamGeometryImpl)PlatformImpl).Open());
+            return new StreamGeometryContext(((IStreamGeometryImpl)PlatformImpl!).Open());
         }
 
         /// <inheritdoc/>
-        protected override IGeometryImpl CreateDefiningGeometry()
+        protected override IGeometryImpl? CreateDefiningGeometry()
         {
             if (_impl == null)
             {
-                var factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+                var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
                 _impl = factory.CreateStreamGeometry();
             }
 
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/GenericTextRunProperties.cs b/src/Avalonia.Visuals/Media/TextFormatting/GenericTextRunProperties.cs
index 7756ca5c8f..13d7b11645 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/GenericTextRunProperties.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/GenericTextRunProperties.cs
@@ -10,9 +10,9 @@ namespace Avalonia.Media.TextFormatting
         private const double DefaultFontRenderingEmSize = 12;
 
         public GenericTextRunProperties(Typeface typeface, double fontRenderingEmSize = DefaultFontRenderingEmSize,
-            TextDecorationCollection textDecorations = null, IBrush foregroundBrush = null,
-            IBrush backgroundBrush = null, BaselineAlignment baselineAlignment = BaselineAlignment.Baseline,
-            CultureInfo cultureInfo = null)
+            TextDecorationCollection? textDecorations = null, IBrush? foregroundBrush = null,
+            IBrush? backgroundBrush = null, BaselineAlignment baselineAlignment = BaselineAlignment.Baseline,
+            CultureInfo? cultureInfo = null)
         {
             Typeface = typeface;
             FontRenderingEmSize = fontRenderingEmSize;
@@ -30,18 +30,18 @@ namespace Avalonia.Media.TextFormatting
         public override double FontRenderingEmSize { get; }
 
         /// <inheritdoc />
-        public override TextDecorationCollection TextDecorations { get; }
+        public override TextDecorationCollection? TextDecorations { get; }
 
         /// <inheritdoc />
-        public override IBrush ForegroundBrush { get; }
+        public override IBrush? ForegroundBrush { get; }
 
         /// <inheritdoc />
-        public override IBrush BackgroundBrush { get; }
+        public override IBrush? BackgroundBrush { get; }
 
         /// <inheritdoc />
         public override BaselineAlignment BaselineAlignment { get; }
 
         /// <inheritdoc />
-        public override CultureInfo CultureInfo { get; }
+        public override CultureInfo? CultureInfo { get; }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/ITextSource.cs b/src/Avalonia.Visuals/Media/TextFormatting/ITextSource.cs
index 0f9994bc65..32012ab8e9 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/ITextSource.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/ITextSource.cs
@@ -10,6 +10,6 @@
         /// </summary>
         /// <param name="textSourceIndex">The text source index.</param>
         /// <returns>The text run.</returns>
-        TextRun GetTextRun(int textSourceIndex);
+        TextRun? GetTextRun(int textSourceIndex);
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/ShapedTextCharacters.cs b/src/Avalonia.Visuals/Media/TextFormatting/ShapedTextCharacters.cs
index 33d1b30e3c..72bb7431d7 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/ShapedTextCharacters.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/ShapedTextCharacters.cs
@@ -166,7 +166,7 @@ namespace Avalonia.Media.TextFormatting
 
         public readonly struct SplitTextCharactersResult
         {
-            public SplitTextCharactersResult(ShapedTextCharacters first, ShapedTextCharacters second)
+            public SplitTextCharactersResult(ShapedTextCharacters first, ShapedTextCharacters? second)
             {
                 First = first;
 
@@ -187,7 +187,7 @@ namespace Avalonia.Media.TextFormatting
             /// <value>
             /// The second text run.
             /// </value>
-            public ShapedTextCharacters Second { get; }
+            public ShapedTextCharacters? Second { get; }
         }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextFormatter.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextFormatter.cs
index e4c898e2b8..d521077a43 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextFormatter.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextFormatter.cs
@@ -41,6 +41,6 @@ namespace Avalonia.Media.TextFormatting
         /// in terms of where the previous line in the paragraph was broken by the text formatting process.</param>
         /// <returns>The formatted line.</returns>
         public abstract TextLine FormatLine(ITextSource textSource, int firstTextSourceIndex, double paragraphWidth,
-            TextParagraphProperties paragraphProperties, TextLineBreak previousLineBreak = null);
+            TextParagraphProperties paragraphProperties, TextLineBreak? previousLineBreak = null);
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextFormatterImpl.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextFormatterImpl.cs
index df63b00c25..7c6af4eaa7 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextFormatterImpl.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextFormatterImpl.cs
@@ -8,7 +8,7 @@ namespace Avalonia.Media.TextFormatting
     {
         /// <inheritdoc cref="TextFormatter.FormatLine"/>
         public override TextLine FormatLine(ITextSource textSource, int firstTextSourceIndex, double paragraphWidth,
-            TextParagraphProperties paragraphProperties, TextLineBreak previousLineBreak = null)
+            TextParagraphProperties paragraphProperties, TextLineBreak? previousLineBreak = null)
         {
             var textWrapping = paragraphProperties.TextWrapping;
 
@@ -241,7 +241,7 @@ namespace Avalonia.Media.TextFormatting
 
                     first.Add(split.First);
 
-                    second.Add(split.Second);
+                    second.Add(split.Second!);
 
                     if (secondCount > 0)
                     {
@@ -269,7 +269,7 @@ namespace Avalonia.Media.TextFormatting
         /// The formatted text runs.
         /// </returns>
         private static List<ShapedTextCharacters> FetchTextRuns(ITextSource textSource,
-            int firstTextSourceIndex, TextLineBreak previousLineBreak, out TextLineBreak nextLineBreak)
+            int firstTextSourceIndex, TextLineBreak? previousLineBreak, out TextLineBreak? nextLineBreak)
         {
             nextLineBreak = default;
 
@@ -277,7 +277,7 @@ namespace Avalonia.Media.TextFormatting
 
             var textRuns = new List<ShapedTextCharacters>();
 
-            if (previousLineBreak != null)
+            if (previousLineBreak?.RemainingCharacters != null)
             {
                 for (var index = 0; index < previousLineBreak.RemainingCharacters.Count; index++)
                 {
@@ -298,11 +298,11 @@ namespace Avalonia.Media.TextFormatting
                         {
                             for (; index < previousLineBreak.RemainingCharacters.Count; index++)
                             {
-                                splitResult.Second.Add(previousLineBreak.RemainingCharacters[index]);
+                                splitResult.Second!.Add(previousLineBreak.RemainingCharacters[index]);
                             }
                         }
 
-                        nextLineBreak = new TextLineBreak(splitResult.Second);
+                        nextLineBreak = new TextLineBreak(splitResult.Second!);
 
                         return splitResult.First;
                     }
@@ -317,7 +317,7 @@ namespace Avalonia.Media.TextFormatting
 
             while (textRunEnumerator.MoveNext())
             {
-                var textRun = textRunEnumerator.Current;
+                var textRun = textRunEnumerator.Current!;
 
                 switch (textRun)
                 {
@@ -346,7 +346,7 @@ namespace Avalonia.Media.TextFormatting
                 {
                     var splitResult = SplitTextRuns(textRuns, currentLength + runLineBreak.PositionWrap);
 
-                    nextLineBreak = new TextLineBreak(splitResult.Second);
+                    nextLineBreak = new TextLineBreak(splitResult.Second!);
 
                     return splitResult.First;
                 }
@@ -398,7 +398,7 @@ namespace Avalonia.Media.TextFormatting
         /// <param name="currentLineBreak">The current line break if the line was explicitly broken.</param>
         /// <returns>The wrapped text line.</returns>
         private static TextLine PerformTextWrapping(List<ShapedTextCharacters> textRuns, TextRange textRange,
-            double paragraphWidth, TextParagraphProperties paragraphProperties, TextLineBreak currentLineBreak)
+            double paragraphWidth, TextParagraphProperties paragraphProperties, TextLineBreak? currentLineBreak)
         {
             var availableWidth = paragraphWidth;
             var currentWidth = 0.0;
@@ -517,7 +517,7 @@ namespace Avalonia.Media.TextFormatting
 
             var lineBreak = remainingCharacters?.Count > 0 ? new TextLineBreak(remainingCharacters) : null;
 
-            if (lineBreak is null && currentLineBreak.TextEndOfLine != null)
+            if (lineBreak is null && currentLineBreak?.TextEndOfLine != null)
             {
                 lineBreak = new TextLineBreak(currentLineBreak.TextEndOfLine);
             }
@@ -553,7 +553,7 @@ namespace Avalonia.Media.TextFormatting
 
         internal readonly struct SplitTextRunsResult
         {
-            public SplitTextRunsResult(List<ShapedTextCharacters> first, List<ShapedTextCharacters> second)
+            public SplitTextRunsResult(List<ShapedTextCharacters> first, List<ShapedTextCharacters>? second)
             {
                 First = first;
 
@@ -574,7 +574,7 @@ namespace Avalonia.Media.TextFormatting
             /// <value>
             /// The second text runs.
             /// </value>
-            public List<ShapedTextCharacters> Second { get; }
+            public List<ShapedTextCharacters>? Second { get; }
         }
 
         private struct TextRunEnumerator
@@ -590,7 +590,7 @@ namespace Avalonia.Media.TextFormatting
             }
 
             // ReSharper disable once MemberHidesStaticFromOuterClass
-            public TextRun Current { get; private set; }
+            public TextRun? Current { get; private set; }
 
             public bool MoveNext()
             {
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextLayout.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextLayout.cs
index a4c9392fa0..40e12c8e99 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextLayout.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextLayout.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Avalonia.Utilities;
 
@@ -14,7 +15,7 @@ namespace Avalonia.Media.TextFormatting
 
         private readonly ReadOnlySlice<char> _text;
         private readonly TextParagraphProperties _paragraphProperties;
-        private readonly IReadOnlyList<ValueSpan<TextRunProperties>> _textStyleOverrides;
+        private readonly IReadOnlyList<ValueSpan<TextRunProperties>>? _textStyleOverrides;
         private readonly TextTrimming _textTrimming;
 
         /// <summary>
@@ -41,12 +42,12 @@ namespace Avalonia.Media.TextFormatting
             TextAlignment textAlignment = TextAlignment.Left,
             TextWrapping textWrapping = TextWrapping.NoWrap,
             TextTrimming textTrimming = TextTrimming.None,
-            TextDecorationCollection textDecorations = null,
+            TextDecorationCollection? textDecorations = null,
             double maxWidth = double.PositiveInfinity,
             double maxHeight = double.PositiveInfinity,
             double lineHeight = double.NaN,
             int maxLines = 0,
-            IReadOnlyList<ValueSpan<TextRunProperties>> textStyleOverrides = null)
+            IReadOnlyList<ValueSpan<TextRunProperties>>? textStyleOverrides = null)
         {
             _text = string.IsNullOrEmpty(text) ?
                 new ReadOnlySlice<char>() :
@@ -228,7 +229,7 @@ namespace Avalonia.Media.TextFormatting
             var currentY = 0d;
 
             var lineIndex = 0;
-            TextLine currentLine = null;
+            TextLine? currentLine = null;
             CharacterHit characterHit;
 
             for (; lineIndex < TextLines.Count; lineIndex++)
@@ -289,7 +290,7 @@ namespace Avalonia.Media.TextFormatting
         /// <returns></returns>
         private static TextParagraphProperties CreateTextParagraphProperties(Typeface typeface, double fontSize,
             IBrush foreground, TextAlignment textAlignment, TextWrapping textWrapping,
-            TextDecorationCollection textDecorations, double lineHeight)
+            TextDecorationCollection? textDecorations, double lineHeight)
         {
             var textRunStyle = new GenericTextRunProperties(typeface, fontSize, textDecorations, foreground);
 
@@ -339,6 +340,7 @@ namespace Avalonia.Media.TextFormatting
         /// <summary>
         /// Updates the layout and applies specified text style overrides.
         /// </summary>
+        [MemberNotNull(nameof(TextLines))]
         private void UpdateLayout()
         {
             if (_text.IsEmpty || MathUtilities.IsZero(MaxWidth) || MathUtilities.IsZero(MaxHeight))
@@ -360,7 +362,7 @@ namespace Avalonia.Media.TextFormatting
                 var textSource = new FormattedTextSource(_text,
                     _paragraphProperties.DefaultTextRunProperties, _textStyleOverrides);
 
-                TextLine previousLine = null;
+                TextLine? previousLine = null;
 
                 while (currentPosition < _text.Length)
                 {
@@ -558,17 +560,17 @@ namespace Avalonia.Media.TextFormatting
         {
             private readonly ReadOnlySlice<char> _text;
             private readonly TextRunProperties _defaultProperties;
-            private readonly IReadOnlyList<ValueSpan<TextRunProperties>> _textModifier;
+            private readonly IReadOnlyList<ValueSpan<TextRunProperties>>? _textModifier;
 
             public FormattedTextSource(ReadOnlySlice<char> text, TextRunProperties defaultProperties,
-                IReadOnlyList<ValueSpan<TextRunProperties>> textModifier)
+                IReadOnlyList<ValueSpan<TextRunProperties>>? textModifier)
             {
                 _text = text;
                 _defaultProperties = defaultProperties;
                 _textModifier = textModifier;
             }
 
-            public TextRun GetTextRun(int textSourceIndex)
+            public TextRun? GetTextRun(int textSourceIndex)
             {
                 if (textSourceIndex > _text.Length)
                 {
@@ -597,7 +599,7 @@ namespace Avalonia.Media.TextFormatting
             /// The created text style run.
             /// </returns>
             private static ValueSpan<TextRunProperties> CreateTextStyleRun(ReadOnlySlice<char> text,
-                TextRunProperties defaultProperties, IReadOnlyList<ValueSpan<TextRunProperties>> textModifier)
+                TextRunProperties defaultProperties, IReadOnlyList<ValueSpan<TextRunProperties>>? textModifier)
             {
                 if (textModifier == null || textModifier.Count == 0)
                 {
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextLine.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextLine.cs
index e343279a43..aea4227002 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextLine.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextLine.cs
@@ -29,7 +29,7 @@ namespace Avalonia.Media.TextFormatting
         /// <returns>
         /// A <see cref="TextLineBreak"/> value that represents the line break.
         /// </returns>
-        public abstract TextLineBreak TextLineBreak { get; }
+        public abstract TextLineBreak? TextLineBreak { get; }
 
         /// <summary>
         /// Gets the distance from the top to the baseline of the current TextLine object.
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextLineBreak.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextLineBreak.cs
index 4ee0a9a28f..d2bd58682a 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextLineBreak.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextLineBreak.cs
@@ -17,11 +17,11 @@ namespace Avalonia.Media.TextFormatting
         /// <summary>
         /// Get the
         /// </summary>
-        public  TextEndOfLine TextEndOfLine { get; }
+        public TextEndOfLine? TextEndOfLine { get; }
 
         /// <summary>
         /// Get the remaining shaped characters that were split up by the <see cref="TextFormatter"/> during the formatting process.
         /// </summary>
-        public IReadOnlyList<ShapedTextCharacters> RemainingCharacters { get; }
+        public IReadOnlyList<ShapedTextCharacters>? RemainingCharacters { get; }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextLineImpl.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextLineImpl.cs
index b68e50c54e..b1397518e4 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextLineImpl.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextLineImpl.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using Avalonia.Media.TextFormatting.Unicode;
 using Avalonia.Platform;
 using Avalonia.Utilities;
@@ -13,7 +14,7 @@ namespace Avalonia.Media.TextFormatting
         private readonly TextLineMetrics _textLineMetrics;
 
         public TextLineImpl(List<ShapedTextCharacters> textRuns, TextRange textRange, double paragraphWidth,
-            TextParagraphProperties paragraphProperties, TextLineBreak lineBreak = null, bool hasCollapsed = false)
+            TextParagraphProperties paragraphProperties, TextLineBreak? lineBreak = null, bool hasCollapsed = false)
         {
             TextRange = textRange;
             TextLineBreak = lineBreak;
@@ -33,7 +34,7 @@ namespace Avalonia.Media.TextFormatting
         public override TextRange TextRange { get; }
 
         /// <inheritdoc/>
-        public override TextLineBreak TextLineBreak { get; }
+        public override TextLineBreak? TextLineBreak { get; }
 
         /// <inheritdoc/>
         public override bool HasCollapsed { get; }
@@ -479,12 +480,13 @@ namespace Avalonia.Media.TextFormatting
         /// </returns>
         internal static ShapedTextCharacters CreateShapedSymbol(TextRun textRun)
         {
-            var formatterImpl = AvaloniaLocator.Current.GetService<ITextShaperImpl>();
+            var properties = textRun.Properties;
 
-            var glyphRun = formatterImpl.ShapeText(textRun.Text, textRun.Properties.Typeface, textRun.Properties.FontRenderingEmSize,
-                textRun.Properties.CultureInfo);
+            _ = properties ?? throw new InvalidOperationException($"{nameof(TextRun.Properties)} should not be null.");
 
-            return new ShapedTextCharacters(glyphRun, textRun.Properties);
+            var glyphRun = TextShaper.Current.ShapeText(textRun.Text, properties.Typeface, properties.FontRenderingEmSize, properties.CultureInfo);
+
+            return new ShapedTextCharacters(glyphRun, properties);
         }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextParagraphProperties.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextParagraphProperties.cs
index 4eff3fbd83..bbff09ad79 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextParagraphProperties.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextParagraphProperties.cs
@@ -44,7 +44,7 @@
         /// If not null, text decorations to apply to all runs in the line. This is in addition
         /// to any text decorations specified by the TextRunProperties for individual text runs.
         /// </summary>
-        public virtual TextDecorationCollection TextDecorations => null;
+        public virtual TextDecorationCollection? TextDecorations => null;
 
         /// <summary>
         /// Gets the text wrapping.
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextRun.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextRun.cs
index 42cb5a7c46..4bfbb89006 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextRun.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextRun.cs
@@ -24,7 +24,7 @@ namespace Avalonia.Media.TextFormatting
         /// <summary>
         /// A set of properties shared by every characters in the run
         /// </summary>
-        public virtual TextRunProperties Properties => null;
+        public virtual TextRunProperties? Properties => null;
 
         private class TextRunDebuggerProxy
         {
@@ -49,7 +49,7 @@ namespace Avalonia.Media.TextFormatting
                 }
             }
 
-            public TextRunProperties Properties => _textRun.Properties;
+            public TextRunProperties? Properties => _textRun.Properties;
         }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextRunProperties.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextRunProperties.cs
index 468df33ab1..513778b596 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextRunProperties.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextRunProperties.cs
@@ -25,29 +25,29 @@ namespace Avalonia.Media.TextFormatting
         ///<summary>
         /// Run TextDecorations. 
         ///</summary>
-        public abstract TextDecorationCollection TextDecorations { get; }
+        public abstract TextDecorationCollection? TextDecorations { get; }
 
         /// <summary>
         /// Brush used to fill text.
         /// </summary>
-        public abstract IBrush ForegroundBrush { get; }
+        public abstract IBrush? ForegroundBrush { get; }
 
         /// <summary>
         /// Brush used to paint background of run.
         /// </summary>
-        public abstract IBrush BackgroundBrush { get; }
+        public abstract IBrush? BackgroundBrush { get; }
 
         /// <summary>
         /// Run text culture.
         /// </summary>
-        public abstract CultureInfo CultureInfo { get; }
+        public abstract CultureInfo? CultureInfo { get; }
 
         /// <summary>
         /// Run vertical box alignment
         /// </summary>
         public abstract BaselineAlignment BaselineAlignment { get; }
 
-        public bool Equals(TextRunProperties other)
+        public bool Equals(TextRunProperties? other)
         {
             if (ReferenceEquals(null, other))
                 return false;
@@ -62,7 +62,7 @@ namespace Avalonia.Media.TextFormatting
                    Equals(CultureInfo, other.CultureInfo);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return ReferenceEquals(this, obj) || obj is TextRunProperties other && Equals(other);
         }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/TextShaper.cs b/src/Avalonia.Visuals/Media/TextFormatting/TextShaper.cs
index a02ace408f..2892e608ab 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/TextShaper.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/TextShaper.cs
@@ -46,7 +46,7 @@ namespace Avalonia.Media.TextFormatting
 
         /// <inheritdoc cref="ITextShaperImpl.ShapeText"/>
         public GlyphRun ShapeText(ReadOnlySlice<char> text, Typeface typeface, double fontRenderingEmSize,
-            CultureInfo culture)
+            CultureInfo? culture)
         {
             return _platformImpl.ShapeText(text, typeface, fontRenderingEmSize, culture);
         }
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/Unicode/LineBreakEnumerator.cs b/src/Avalonia.Visuals/Media/TextFormatting/Unicode/LineBreakEnumerator.cs
index 40891a700d..0f6b81975a 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/Unicode/LineBreakEnumerator.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/Unicode/LineBreakEnumerator.cs
@@ -80,12 +80,12 @@ namespace Avalonia.Media.TextFormatting.Unicode
                     }
                 }
 
-                var shouldBreak = GetSimpleBreak() ?? (bool?)GetPairTableBreak(lastClass);
+                var shouldBreak = GetSimpleBreak() ?? GetPairTableBreak(lastClass);
 
                 // Rule LB8a
                 _lb8a = _nextClass == LineBreakClass.ZWJ;
 
-                if (shouldBreak.Value)
+                if (shouldBreak)
                 {
                     Current = new LineBreak(FindPriorNonWhitespace(_lastPosition), _lastPosition);
                     return true;
diff --git a/src/Avalonia.Visuals/Media/TextFormatting/Unicode/UnicodeData.cs b/src/Avalonia.Visuals/Media/TextFormatting/Unicode/UnicodeData.cs
index 3c00c49707..4189b24af6 100644
--- a/src/Avalonia.Visuals/Media/TextFormatting/Unicode/UnicodeData.cs
+++ b/src/Avalonia.Visuals/Media/TextFormatting/Unicode/UnicodeData.cs
@@ -24,8 +24,8 @@
 
         static UnicodeData()
         {
-            s_unicodeDataTrie = new UnicodeTrie(typeof(UnicodeData).Assembly.GetManifestResourceStream("Avalonia.Assets.UnicodeData.trie"));
-            s_graphemeBreakTrie = new UnicodeTrie(typeof(UnicodeData).Assembly.GetManifestResourceStream("Avalonia.Assets.GraphemeBreak.trie"));
+            s_unicodeDataTrie = new UnicodeTrie(typeof(UnicodeData).Assembly.GetManifestResourceStream("Avalonia.Assets.UnicodeData.trie")!);
+            s_graphemeBreakTrie = new UnicodeTrie(typeof(UnicodeData).Assembly.GetManifestResourceStream("Avalonia.Assets.GraphemeBreak.trie")!);
         }
 
         /// <summary>
diff --git a/src/Avalonia.Visuals/Media/Transform.cs b/src/Avalonia.Visuals/Media/Transform.cs
index 7cf1b35ada..60701ecfaf 100644
--- a/src/Avalonia.Visuals/Media/Transform.cs
+++ b/src/Avalonia.Visuals/Media/Transform.cs
@@ -19,7 +19,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Raised when the transform changes.
         /// </summary>
-        public event EventHandler Changed;
+        public event EventHandler? Changed;
 
         /// <summary>
         /// Gets the transform's <see cref="Matrix"/>.
diff --git a/src/Avalonia.Visuals/Media/TransformConverter.cs b/src/Avalonia.Visuals/Media/TransformConverter.cs
index e79c0b8b7b..33c6cd10fb 100644
--- a/src/Avalonia.Visuals/Media/TransformConverter.cs
+++ b/src/Avalonia.Visuals/Media/TransformConverter.cs
@@ -10,14 +10,14 @@ namespace Avalonia.Media
     /// </summary>
     public class TransformConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
         {
-            return TransformOperations.Parse((string)value);
+            return value is string s ? TransformOperations.Parse(s) : null;
         }
     }
 }
diff --git a/src/Avalonia.Visuals/Media/TransformGroup.cs b/src/Avalonia.Visuals/Media/TransformGroup.cs
index 8e3cfec274..0465efd5a5 100644
--- a/src/Avalonia.Visuals/Media/TransformGroup.cs
+++ b/src/Avalonia.Visuals/Media/TransformGroup.cs
@@ -24,7 +24,7 @@ namespace Avalonia.Media
             };
         }
 
-        private void ChildTransform_Changed(object sender, System.EventArgs e)
+        private void ChildTransform_Changed(object? sender, System.EventArgs e)
         {
             this.RaiseChanged();
         }
diff --git a/src/Avalonia.Visuals/Media/Transformation/TransformOperation.cs b/src/Avalonia.Visuals/Media/Transformation/TransformOperation.cs
index 13a24cd523..a8c0fe9b12 100644
--- a/src/Avalonia.Visuals/Media/Transformation/TransformOperation.cs
+++ b/src/Avalonia.Visuals/Media/Transformation/TransformOperation.cs
@@ -92,8 +92,8 @@ namespace Avalonia.Media.Transformation
             }
 
             // ReSharper disable PossibleInvalidOperationException
-            TransformOperation fromValue = fromIdentity ? Identity : from.Value;
-            TransformOperation toValue = toIdentity ? Identity : to.Value;
+            TransformOperation fromValue = fromIdentity ? Identity : from!.Value;
+            TransformOperation toValue = toIdentity ? Identity : to!.Value;
             // ReSharper restore PossibleInvalidOperationException
 
             var interpolationType = toIdentity ? fromValue.Type : toValue.Type;
diff --git a/src/Avalonia.Visuals/Media/Typeface.cs b/src/Avalonia.Visuals/Media/Typeface.cs
index 17824c3c5e..8245b63440 100644
--- a/src/Avalonia.Visuals/Media/Typeface.cs
+++ b/src/Avalonia.Visuals/Media/Typeface.cs
@@ -48,7 +48,7 @@ namespace Avalonia.Media
         /// <summary>
         /// Gets the font family.
         /// </summary>
-        public FontFamily FontFamily { get; }
+        public FontFamily? FontFamily { get; }
 
         /// <summary>
         /// Gets the font style.
@@ -78,7 +78,7 @@ namespace Avalonia.Media
             return  a.Equals(b);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is Typeface typeface && Equals(typeface);
         }
diff --git a/src/Avalonia.Visuals/Media/UnicodeRange.cs b/src/Avalonia.Visuals/Media/UnicodeRange.cs
index 6179b57ece..0077dd64ac 100644
--- a/src/Avalonia.Visuals/Media/UnicodeRange.cs
+++ b/src/Avalonia.Visuals/Media/UnicodeRange.cs
@@ -12,7 +12,7 @@ namespace Avalonia.Media
         public static UnicodeRange Default = Parse("0-10FFFD");
 
         private readonly UnicodeRangeSegment _single;
-        private readonly IReadOnlyList<UnicodeRangeSegment> _segments = null;
+        private readonly IReadOnlyList<UnicodeRangeSegment>? _segments = null;
 
         public UnicodeRange(int start, int end)
         {
@@ -37,7 +37,7 @@ namespace Avalonia.Media
 
         internal UnicodeRangeSegment Single => _single;
 
-        internal IReadOnlyList<UnicodeRangeSegment> Segments => _segments;
+        internal IReadOnlyList<UnicodeRangeSegment>? Segments => _segments;
 
         /// <summary>
         /// Determines if given value is inside the range.
diff --git a/src/Avalonia.Visuals/Platform/ExportRenderingSubsystemAttribute.cs b/src/Avalonia.Visuals/Platform/ExportRenderingSubsystemAttribute.cs
index 57f9c68456..db157304f4 100644
--- a/src/Avalonia.Visuals/Platform/ExportRenderingSubsystemAttribute.cs
+++ b/src/Avalonia.Visuals/Platform/ExportRenderingSubsystemAttribute.cs
@@ -6,7 +6,7 @@ namespace Avalonia.Platform
     public class ExportRenderingSubsystemAttribute : Attribute
     {
         public ExportRenderingSubsystemAttribute(OperatingSystemType requiredOS, int priority, string name, Type initializationType, string initializationMethod,
-            Type environmentChecker = null)
+            Type? environmentChecker = null)
         {
             Name = name;
             InitializationType = initializationType;
@@ -17,11 +17,11 @@ namespace Avalonia.Platform
         }
 
         public string InitializationMethod { get; private set; }
-        public Type EnvironmentChecker { get; }
+        public Type? EnvironmentChecker { get; }
         public Type InitializationType { get; private set; }
         public string Name { get; private set; }
         public int Priority { get; private set; }
         public OperatingSystemType RequiredOS { get; private set; }
-        public string RequiresWindowingSubsystem { get; set; }
+        public string? RequiresWindowingSubsystem { get; set; }
     }
 }
diff --git a/src/Avalonia.Visuals/Platform/IDrawingContextImpl.cs b/src/Avalonia.Visuals/Platform/IDrawingContextImpl.cs
index ac2c5c9f08..a1f42c171c 100644
--- a/src/Avalonia.Visuals/Platform/IDrawingContextImpl.cs
+++ b/src/Avalonia.Visuals/Platform/IDrawingContextImpl.cs
@@ -55,7 +55,7 @@ namespace Avalonia.Platform
         /// <param name="brush">The fill brush.</param>
         /// <param name="pen">The stroke pen.</param>
         /// <param name="geometry">The geometry.</param>
-        void DrawGeometry(IBrush brush, IPen pen, IGeometryImpl geometry);
+        void DrawGeometry(IBrush? brush, IPen? pen, IGeometryImpl geometry);
 
         /// <summary>
         /// Draws a rectangle with the specified Brush and Pen.
@@ -68,7 +68,7 @@ namespace Avalonia.Platform
         /// The brush and the pen can both be null. If the brush is null, then no fill is performed.
         /// If the pen is null, then no stoke is performed. If both the pen and the brush are null, then the drawing is not visible.
         /// </remarks>
-        void DrawRectangle(IBrush brush, IPen pen, RoundedRect rect,
+        void DrawRectangle(IBrush? brush, IPen? pen, RoundedRect rect,
             BoxShadows boxShadows = default);
 
         /// <summary>
@@ -81,7 +81,7 @@ namespace Avalonia.Platform
         /// The brush and the pen can both be null. If the brush is null, then no fill is performed.
         /// If the pen is null, then no stoke is performed. If both the pen and the brush are null, then the drawing is not visible.
         /// </remarks>
-        void DrawEllipse(IBrush brush, IPen pen, Rect rect);
+        void DrawEllipse(IBrush? brush, IPen? pen, Rect rect);
 
         /// <summary>
         /// Draws text.
diff --git a/src/Avalonia.Visuals/Platform/IFontManagerImpl.cs b/src/Avalonia.Visuals/Platform/IFontManagerImpl.cs
index e562b45ca8..113c72d373 100644
--- a/src/Avalonia.Visuals/Platform/IFontManagerImpl.cs
+++ b/src/Avalonia.Visuals/Platform/IFontManagerImpl.cs
@@ -31,7 +31,7 @@ namespace Avalonia.Platform
         /// </returns>
         bool TryMatchCharacter(int codepoint, FontStyle fontStyle,
             FontWeight fontWeight,
-            FontFamily fontFamily, CultureInfo culture, out Typeface typeface);
+            FontFamily? fontFamily, CultureInfo? culture, out Typeface typeface);
 
         /// <summary>
         ///     Creates a glyph typeface.
diff --git a/src/Avalonia.Visuals/Platform/IGeometryImpl.cs b/src/Avalonia.Visuals/Platform/IGeometryImpl.cs
index 79e125c5cb..ed6de1b5c7 100644
--- a/src/Avalonia.Visuals/Platform/IGeometryImpl.cs
+++ b/src/Avalonia.Visuals/Platform/IGeometryImpl.cs
@@ -23,7 +23,7 @@ namespace Avalonia.Platform
         /// </summary>
         /// <param name="pen">The pen to use. May be null.</param>
         /// <returns>The bounding rectangle.</returns>
-        Rect GetRenderBounds(IPen pen);
+        Rect GetRenderBounds(IPen? pen);
 
         /// <summary>
         /// Indicates whether the geometry's fill contains the specified point.
diff --git a/src/Avalonia.Visuals/Platform/IPlatformRenderInterface.cs b/src/Avalonia.Visuals/Platform/IPlatformRenderInterface.cs
index 772f1ac9f3..60ae0b5ef8 100644
--- a/src/Avalonia.Visuals/Platform/IPlatformRenderInterface.cs
+++ b/src/Avalonia.Visuals/Platform/IPlatformRenderInterface.cs
@@ -29,7 +29,7 @@ namespace Avalonia.Platform
             TextAlignment textAlignment,
             TextWrapping wrapping,
             Size constraint,
-            IReadOnlyList<FormattedTextStyleSpan> spans);
+            IReadOnlyList<FormattedTextStyleSpan>? spans);
 
         /// <summary>
         /// Creates an ellipse geometry implementation.
diff --git a/src/Avalonia.Visuals/Platform/IRenderTarget.cs b/src/Avalonia.Visuals/Platform/IRenderTarget.cs
index 68b3b4c17d..7023f2ca51 100644
--- a/src/Avalonia.Visuals/Platform/IRenderTarget.cs
+++ b/src/Avalonia.Visuals/Platform/IRenderTarget.cs
@@ -18,7 +18,7 @@ namespace Avalonia.Platform
         /// A render to be used to render visual brushes. May be null if no visual brushes are
         /// to be drawn.
         /// </param>
-        IDrawingContextImpl CreateDrawingContext(IVisualBrushRenderer visualBrushRenderer);
+        IDrawingContextImpl CreateDrawingContext(IVisualBrushRenderer? visualBrushRenderer);
     }
 
     public interface IRenderTargetWithCorruptionInfo : IRenderTarget
diff --git a/src/Avalonia.Visuals/Platform/ITextShaperImpl.cs b/src/Avalonia.Visuals/Platform/ITextShaperImpl.cs
index d915da2603..73d198d7ef 100644
--- a/src/Avalonia.Visuals/Platform/ITextShaperImpl.cs
+++ b/src/Avalonia.Visuals/Platform/ITextShaperImpl.cs
@@ -17,6 +17,6 @@ namespace Avalonia.Platform
         /// <param name="fontRenderingEmSize">The font rendering em size.</param>
         /// <param name="culture">The culture.</param>
         /// <returns>A shaped glyph run.</returns>
-        GlyphRun ShapeText(ReadOnlySlice<char> text, Typeface typeface, double fontRenderingEmSize, CultureInfo culture);
+        GlyphRun ShapeText(ReadOnlySlice<char> text, Typeface typeface, double fontRenderingEmSize, CultureInfo? culture);
     }
 }
diff --git a/src/Avalonia.Visuals/Platform/PathGeometryContext.cs b/src/Avalonia.Visuals/Platform/PathGeometryContext.cs
index 391a43d1cf..694e9f8d80 100644
--- a/src/Avalonia.Visuals/Platform/PathGeometryContext.cs
+++ b/src/Avalonia.Visuals/Platform/PathGeometryContext.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Avalonia.Media;
 using Avalonia.Platform;
 
@@ -6,8 +7,8 @@ namespace Avalonia.Visuals.Platform
 {
     public class PathGeometryContext : IGeometryContext
     {
-        private PathFigure _currentFigure;
-        private PathGeometry _pathGeometry;
+        private PathFigure? _currentFigure;
+        private PathGeometry? _pathGeometry;
 
         public PathGeometryContext(PathGeometry pathGeometry)
         {
@@ -30,13 +31,16 @@ namespace Avalonia.Visuals.Platform
                 Point = point
             };
 
-            _currentFigure.Segments.Add(arcSegment);
+            CurrentFigureSegments().Add(arcSegment);
         }
 
         public void BeginFigure(Point startPoint, bool isFilled)
         {
+            ThrowIfDisposed();
+
             _currentFigure = new PathFigure { StartPoint = startPoint, IsClosed = false, IsFilled = isFilled };
 
+            _pathGeometry.Figures ??= new();
             _pathGeometry.Figures.Add(_currentFigure);
         }
 
@@ -44,14 +48,14 @@ namespace Avalonia.Visuals.Platform
         {
             var bezierSegment = new BezierSegment { Point1 = point1, Point2 = point2, Point3 = point3 };
 
-            _currentFigure.Segments.Add(bezierSegment);
+            CurrentFigureSegments().Add(bezierSegment);
         }
 
         public void QuadraticBezierTo(Point control, Point endPoint)
         {
             var quadraticBezierSegment = new QuadraticBezierSegment { Point1 = control, Point2 = endPoint };
 
-            _currentFigure.Segments.Add(quadraticBezierSegment);
+            CurrentFigureSegments().Add(quadraticBezierSegment);
         }
 
         public void LineTo(Point point)
@@ -61,7 +65,7 @@ namespace Avalonia.Visuals.Platform
                 Point = point
             };
 
-            _currentFigure.Segments.Add(lineSegment);
+            CurrentFigureSegments().Add(lineSegment);
         }
 
         public void EndFigure(bool isClosed)
@@ -76,7 +80,26 @@ namespace Avalonia.Visuals.Platform
 
         public void SetFillRule(FillRule fillRule)
         {
+            ThrowIfDisposed();
             _pathGeometry.FillRule = fillRule;
         }
+
+        [MemberNotNull(nameof(_pathGeometry))]
+        private void ThrowIfDisposed()
+        {
+            if (_pathGeometry is null)
+                throw new ObjectDisposedException(nameof(PathGeometryContext));
+        }
+
+        private PathSegments CurrentFigureSegments()
+        {
+            ThrowIfDisposed();
+
+            if (_currentFigure is null)
+                throw new InvalidOperationException("No figure in progress.");
+            if (_currentFigure.Segments is null)
+                throw new InvalidOperationException("Current figure's segments cannot be null.");
+            return _currentFigure.Segments;
+        }
     }
 }
diff --git a/src/Avalonia.Visuals/Point.cs b/src/Avalonia.Visuals/Point.cs
index 6febe9c802..67e7d71fbc 100644
--- a/src/Avalonia.Visuals/Point.cs
+++ b/src/Avalonia.Visuals/Point.cs
@@ -211,7 +211,7 @@ namespace Avalonia
         /// <returns>
         /// True if <paramref name="obj"/> is a point that equals the current point.
         /// </returns>
-        public override bool Equals(object obj) => obj is Point other && Equals(other);
+        public override bool Equals(object? obj) => obj is Point other && Equals(other);
 
         /// <summary>
         /// Returns a hash code for a <see cref="Point"/>.
diff --git a/src/Avalonia.Visuals/Rect.cs b/src/Avalonia.Visuals/Rect.cs
index d2a72db6ae..6d7d6c2e54 100644
--- a/src/Avalonia.Visuals/Rect.cs
+++ b/src/Avalonia.Visuals/Rect.cs
@@ -341,7 +341,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="obj">The object to compare against.</param>
         /// <returns>True if the object is equal to this rectangle; false otherwise.</returns>
-        public override bool Equals(object obj) => obj is Rect other && Equals(other);
+        public override bool Equals(object? obj) => obj is Rect other && Equals(other);
 
         /// <summary>
         /// Returns the hash code for this instance.
diff --git a/src/Avalonia.Visuals/RelativePoint.cs b/src/Avalonia.Visuals/RelativePoint.cs
index 497820ec65..4550dbd54b 100644
--- a/src/Avalonia.Visuals/RelativePoint.cs
+++ b/src/Avalonia.Visuals/RelativePoint.cs
@@ -111,7 +111,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="obj">The other object.</param>
         /// <returns>True if the objects are equal, otherwise false.</returns>
-        public override bool Equals(object obj) => obj is RelativePoint other && Equals(other);
+        public override bool Equals(object? obj) => obj is RelativePoint other && Equals(other);
 
         /// <summary>
         /// Checks if the <see cref="RelativePoint"/> equals another point.
diff --git a/src/Avalonia.Visuals/RelativeRect.cs b/src/Avalonia.Visuals/RelativeRect.cs
index 1d1f53e299..f6eb257c85 100644
--- a/src/Avalonia.Visuals/RelativeRect.cs
+++ b/src/Avalonia.Visuals/RelativeRect.cs
@@ -113,7 +113,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="obj">The other object.</param>
         /// <returns>True if the objects are equal, otherwise false.</returns>
-        public override bool Equals(object obj) => obj is RelativeRect other && Equals(other);
+        public override bool Equals(object? obj) => obj is RelativeRect other && Equals(other);
 
         /// <summary>
         /// Checks if the <see cref="RelativeRect"/> equals another rectangle.
diff --git a/src/Avalonia.Visuals/Rendering/DefaultRenderTimer.cs b/src/Avalonia.Visuals/Rendering/DefaultRenderTimer.cs
index 8d6c3e67c1..82d3892975 100644
--- a/src/Avalonia.Visuals/Rendering/DefaultRenderTimer.cs
+++ b/src/Avalonia.Visuals/Rendering/DefaultRenderTimer.cs
@@ -14,10 +14,10 @@ namespace Avalonia.Rendering
     /// </remarks>
     public class DefaultRenderTimer : IRenderTimer
     {
-        private IRuntimePlatform _runtime;
+        private IRuntimePlatform? _runtime;
         private int _subscriberCount;
-        private Action<TimeSpan> _tick;
-        private IDisposable _subscription;
+        private Action<TimeSpan>? _tick;
+        private IDisposable? _subscription;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="DefaultRenderTimer"/> class.
@@ -77,10 +77,7 @@ namespace Avalonia.Rendering
         /// </remarks>
         protected virtual IDisposable StartCore(Action<TimeSpan> tick)
         {
-            if (_runtime == null)
-            {
-                _runtime = AvaloniaLocator.Current.GetService<IRuntimePlatform>();
-            }
+            _runtime ??= AvaloniaLocator.Current.GetRequiredService<IRuntimePlatform>();
 
             return _runtime.StartSystemTimer(
                 TimeSpan.FromSeconds(1.0 / FramesPerSecond),
@@ -92,13 +89,13 @@ namespace Avalonia.Rendering
         /// </summary>
         protected void Stop()
         {
-            _subscription.Dispose();
+            _subscription?.Dispose();
             _subscription = null;
         }
 
         private void InternalTick(TimeSpan tickCount)
         {
-            _tick(tickCount);
+            _tick?.Invoke(tickCount);
         }
     }
 }
diff --git a/src/Avalonia.Visuals/Rendering/DeferredRenderer.cs b/src/Avalonia.Visuals/Rendering/DeferredRenderer.cs
index fe63fdec46..7b9c515b97 100644
--- a/src/Avalonia.Visuals/Rendering/DeferredRenderer.cs
+++ b/src/Avalonia.Visuals/Rendering/DeferredRenderer.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using Avalonia.Logging;
@@ -19,20 +20,20 @@ namespace Avalonia.Rendering
     /// </summary>
     public class DeferredRenderer : RendererBase, IRenderer, IRenderLoopTask, IVisualBrushRenderer
     {
-        private readonly IDispatcher _dispatcher;
-        private readonly IRenderLoop _renderLoop;
+        private readonly IDispatcher? _dispatcher;
+        private readonly IRenderLoop? _renderLoop;
         private readonly IVisual _root;
         private readonly ISceneBuilder _sceneBuilder;
 
         private bool _running;
         private bool _disposed;
-        private volatile IRef<Scene> _scene;
-        private DirtyVisuals _dirty;
-        private HashSet<IVisual> _recalculateChildren;
-        private IRef<IRenderTargetBitmapImpl> _overlay;
+        private volatile IRef<Scene>? _scene;
+        private DirtyVisuals? _dirty;
+        private HashSet<IVisual>? _recalculateChildren;
+        private IRef<IRenderTargetBitmapImpl>? _overlay;
         private int _lastSceneId = -1;
         private DisplayDirtyRects _dirtyRectsDisplay = new DisplayDirtyRects();
-        private IRef<IDrawOperation> _currentDraw;
+        private IRef<IDrawOperation>? _currentDraw;
         private readonly IDeferredRendererLock _lock;
         private readonly object _sceneLock = new object();
         private readonly object _startStopLock = new object();
@@ -50,14 +51,12 @@ namespace Avalonia.Rendering
         public DeferredRenderer(
             IRenderRoot root,
             IRenderLoop renderLoop,
-            ISceneBuilder sceneBuilder = null,
-            IDispatcher dispatcher = null,
-            IDeferredRendererLock rendererLock = null) : base(true)
+            ISceneBuilder? sceneBuilder = null,
+            IDispatcher? dispatcher = null,
+            IDeferredRendererLock? rendererLock = null) : base(true)
         {
-            Contract.Requires<ArgumentNullException>(root != null);
-
             _dispatcher = dispatcher ?? Dispatcher.UIThread;
-            _root = root;
+            _root = root ?? throw new ArgumentNullException(nameof(root));
             _sceneBuilder = sceneBuilder ?? new SceneBuilder();
             Layers = new RenderLayers();
             _renderLoop = renderLoop;
@@ -77,13 +76,10 @@ namespace Avalonia.Rendering
         public DeferredRenderer(
             IVisual root,
             IRenderTarget renderTarget,
-            ISceneBuilder sceneBuilder = null) : base(true)
+            ISceneBuilder? sceneBuilder = null) : base(true)
         {
-            Contract.Requires<ArgumentNullException>(root != null);
-            Contract.Requires<ArgumentNullException>(renderTarget != null);
-
-            _root = root;
-            RenderTarget = renderTarget;
+            _root = root ?? throw new ArgumentNullException(nameof(root));
+            RenderTarget = renderTarget ?? throw new ArgumentNullException(nameof(renderTarget));
             _sceneBuilder = sceneBuilder ?? new SceneBuilder();
             Layers = new RenderLayers();
             _lock = new ManagedDeferredRendererLock();
@@ -99,7 +95,7 @@ namespace Avalonia.Rendering
         /// <summary>
         /// Gets or sets a path to which rendered frame should be rendered for debugging.
         /// </summary>
-        public string DebugFramesPath { get; set; }
+        public string? DebugFramesPath { get; set; }
 
         /// <summary>
         /// Forces the renderer to only draw frames on the render thread. Makes Paint to wait until frame is rendered
@@ -107,7 +103,7 @@ namespace Avalonia.Rendering
         public bool RenderOnlyOnRenderThread { get; set; }
 
         /// <inheritdoc/>
-        public event EventHandler<SceneInvalidatedEventArgs> SceneInvalidated;
+        public event EventHandler<SceneInvalidatedEventArgs>? SceneInvalidated;
 
         /// <summary>
         /// Gets the render layers.
@@ -117,7 +113,7 @@ namespace Avalonia.Rendering
         /// <summary>
         /// Gets the current render target.
         /// </summary>
-        internal IRenderTarget RenderTarget { get; private set; }
+        internal IRenderTarget? RenderTarget { get; private set; }
 
         /// <inheritdoc/>
         public void AddDirty(IVisual visual)
@@ -167,7 +163,7 @@ namespace Avalonia.Rendering
         }
 
         /// <inheritdoc/>
-        public IEnumerable<IVisual> HitTest(Point p, IVisual root, Func<IVisual, bool> filter)
+        public IEnumerable<IVisual> HitTest(Point p, IVisual root, Func<IVisual, bool>? filter)
         {
             EnsureCanHitTest();
 
@@ -177,7 +173,7 @@ namespace Avalonia.Rendering
         }
 
         /// <inheritdoc/>
-        public IVisual HitTestFirst(Point p, IVisual root, Func<IVisual, bool> filter)
+        public IVisual? HitTestFirst(Point p, IVisual root, Func<IVisual, bool>? filter)
         {
             EnsureCanHitTest();
 
@@ -199,7 +195,7 @@ namespace Avalonia.Rendering
                 
                 while (true)
                 {
-                    Scene scene;
+                    Scene? scene;
                     bool? updated;
                     lock (_sceneLock)
                     {
@@ -297,7 +293,7 @@ namespace Avalonia.Rendering
 
         internal void UnitTestRender() => Render(false);
 
-        internal Scene UnitTestScene() => _scene.Item;
+        internal Scene? UnitTestScene() => _scene?.Item;
 
         private void EnsureCanHitTest()
         {
@@ -315,7 +311,7 @@ namespace Avalonia.Rendering
                 if (l == null)
                     return;
 
-                IDrawingContextImpl context = null;
+                IDrawingContextImpl? context = null;
                 try
                 {
                     try
@@ -358,10 +354,10 @@ namespace Avalonia.Rendering
             }
         }
 
-        private (IRef<Scene> scene, bool updated) UpdateRenderLayersAndConsumeSceneIfNeeded(ref IDrawingContextImpl context,
+        private (IRef<Scene>? scene, bool updated) UpdateRenderLayersAndConsumeSceneIfNeeded(ref IDrawingContextImpl? context,
             bool recursiveCall = false)
         {
-            IRef<Scene> sceneRef;
+            IRef<Scene>? sceneRef;
             lock (_sceneLock)
                 sceneRef = _scene?.Clone();
             if (sceneRef == null)
@@ -416,7 +412,7 @@ namespace Avalonia.Rendering
         }
 
 
-        private void Render(IDrawingContextImpl context, VisualNode node, IVisual layer, Rect clipBounds)
+        private void Render(IDrawingContextImpl context, VisualNode node, IVisual? layer, Rect clipBounds)
         {
             if (layer == null || node.LayerRoot == layer)
             {
@@ -459,7 +455,7 @@ namespace Avalonia.Rendering
                 if (layer.Dirty.IsEmpty && !renderLayer.IsEmpty)
                     continue;
                 var renderTarget = renderLayer.Bitmap;
-                var node = (VisualNode)scene.FindNode(layer.LayerRoot);
+                var node = (VisualNode?)scene.FindNode(layer.LayerRoot);
 
                 if (node != null)
                 {
@@ -515,7 +511,7 @@ namespace Avalonia.Rendering
                     Math.Ceiling(rect.Bottom * scale) / scale));
         }
 
-        private void RenderOverlay(Scene scene, ref IDrawingContextImpl parentContent)
+        private void RenderOverlay(Scene scene, ref IDrawingContextImpl? parentContent)
         {
             EnsureDrawingContext(ref parentContent);
 
@@ -545,7 +541,7 @@ namespace Avalonia.Rendering
             }
         }
 
-        private void RenderComposite(Scene scene, ref IDrawingContextImpl context)
+        private void RenderComposite(Scene scene, ref IDrawingContextImpl? context)
         {
             EnsureDrawingContext(ref context);
 
@@ -596,7 +592,7 @@ namespace Avalonia.Rendering
             }
         }
 
-        private void EnsureDrawingContext(ref IDrawingContextImpl context)
+        private void EnsureDrawingContext([NotNull] ref IDrawingContextImpl? context)
         {
             if (context != null)
             {
@@ -605,7 +601,7 @@ namespace Avalonia.Rendering
 
             if ((RenderTarget as IRenderTargetWithCorruptionInfo)?.IsCorrupted == true)
             {
-                RenderTarget.Dispose();
+                RenderTarget!.Dispose();
                 RenderTarget = null;
             }
 
@@ -647,10 +643,10 @@ namespace Avalonia.Rendering
                 }
                 else
                 {
-                    foreach (var visual in _recalculateChildren)
+                    foreach (var visual in _recalculateChildren!)
                     {
                         var node = scene.FindNode(visual);
-                        ((VisualNode)node)?.SortChildren(scene);
+                        ((VisualNode?)node)?.SortChildren(scene);
                     }
 
                     _recalculateChildren.Clear();
@@ -724,7 +720,7 @@ namespace Avalonia.Rendering
 
             foreach (var layer in Layers)
             {
-                var fileName = Path.Combine(DebugFramesPath, $"frame-{id}-layer-{index++}.png");
+                var fileName = Path.Combine(DebugFramesPath ?? string.Empty, $"frame-{id}-layer-{index++}.png");
                 layer.Bitmap.Item.Save(fileName);
             }
         }
diff --git a/src/Avalonia.Visuals/Rendering/IDeferredRendererLock.cs b/src/Avalonia.Visuals/Rendering/IDeferredRendererLock.cs
index b2ed3afe6a..eab3dca58e 100644
--- a/src/Avalonia.Visuals/Rendering/IDeferredRendererLock.cs
+++ b/src/Avalonia.Visuals/Rendering/IDeferredRendererLock.cs
@@ -4,6 +4,6 @@ namespace Avalonia.Rendering
 {
     public interface IDeferredRendererLock
     {
-        IDisposable TryLock();
+        IDisposable? TryLock();
     }
 }
diff --git a/src/Avalonia.Visuals/Rendering/IRenderer.cs b/src/Avalonia.Visuals/Rendering/IRenderer.cs
index 0c7440d159..e998f78d5c 100644
--- a/src/Avalonia.Visuals/Rendering/IRenderer.cs
+++ b/src/Avalonia.Visuals/Rendering/IRenderer.cs
@@ -27,7 +27,7 @@ namespace Avalonia.Rendering
         /// Indicates that the underlying low-level scene information has been updated. Used to
         /// signal that an update to the current pointer-over state may be required.
         /// </remarks>
-        event EventHandler<SceneInvalidatedEventArgs> SceneInvalidated;
+        event EventHandler<SceneInvalidatedEventArgs>? SceneInvalidated;
 
         /// <summary>
         /// Mark a visual as dirty and needing re-rendering.
@@ -57,7 +57,7 @@ namespace Avalonia.Rendering
         /// children will be excluded from the results.
         /// </param>
         /// <returns>The visual at the specified point, topmost first.</returns>
-        IVisual HitTestFirst(Point p, IVisual root, Func<IVisual, bool> filter);
+        IVisual? HitTestFirst(Point p, IVisual root, Func<IVisual, bool> filter);
 
         /// <summary>
         /// Informs the renderer that the z-ordering of a visual's children has changed.
diff --git a/src/Avalonia.Visuals/Rendering/ImmediateRenderer.cs b/src/Avalonia.Visuals/Rendering/ImmediateRenderer.cs
index 88fbd290e6..f6642102f7 100644
--- a/src/Avalonia.Visuals/Rendering/ImmediateRenderer.cs
+++ b/src/Avalonia.Visuals/Rendering/ImmediateRenderer.cs
@@ -19,9 +19,9 @@ namespace Avalonia.Rendering
     public class ImmediateRenderer : RendererBase, IRenderer, IVisualBrushRenderer
     {
         private readonly IVisual _root;
-        private readonly IRenderRoot _renderRoot;
+        private readonly IRenderRoot? _renderRoot;
         private bool _updateTransformedBounds = true;
-        private IRenderTarget _renderTarget;
+        private IRenderTarget? _renderTarget;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ImmediateRenderer"/> class.
@@ -29,9 +29,7 @@ namespace Avalonia.Rendering
         /// <param name="root">The control to render.</param>
         public ImmediateRenderer(IVisual root)
         {
-            Contract.Requires<ArgumentNullException>(root != null);
-
-            _root = root;
+            _root = root ?? throw new ArgumentNullException(nameof(root));
             _renderRoot = root as IRenderRoot;
         }
 
@@ -49,7 +47,7 @@ namespace Avalonia.Rendering
         public bool DrawDirtyRects { get; set; }
 
         /// <inheritdoc/>
-        public event EventHandler<SceneInvalidatedEventArgs> SceneInvalidated;
+        public event EventHandler<SceneInvalidatedEventArgs>? SceneInvalidated;
 
         /// <inheritdoc/>
         public void Paint(Rect rect)
@@ -169,7 +167,7 @@ namespace Avalonia.Rendering
             return HitTest(root, p, filter);
         }
 
-        public IVisual HitTestFirst(Point p, IVisual root, Func<IVisual, bool> filter)
+        public IVisual? HitTestFirst(Point p, IVisual root, Func<IVisual, bool> filter)
         {
             return HitTest(root, p, filter).FirstOrDefault();
         }
@@ -233,9 +231,9 @@ namespace Avalonia.Rendering
         private static IEnumerable<IVisual> HitTest(
            IVisual visual,
            Point p,
-           Func<IVisual, bool> filter)
+           Func<IVisual, bool>? filter)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             if (filter?.Invoke(visual) != false)
             {
diff --git a/src/Avalonia.Visuals/Rendering/RenderLayers.cs b/src/Avalonia.Visuals/Rendering/RenderLayers.cs
index e82934fbad..7583886835 100644
--- a/src/Avalonia.Visuals/Rendering/RenderLayers.cs
+++ b/src/Avalonia.Visuals/Rendering/RenderLayers.cs
@@ -1,5 +1,6 @@
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using Avalonia.Platform;
 using Avalonia.Rendering.SceneGraph;
 using Avalonia.VisualTree;
@@ -19,9 +20,8 @@ namespace Avalonia.Rendering
             for (var i = scene.Layers.Count - 1; i >= 0; --i)
             {
                 var src = scene.Layers[i];
-                RenderLayer layer;
 
-                if (!_index.TryGetValue(src.LayerRoot, out layer))
+                if (!_index.TryGetValue(src.LayerRoot, out var layer))
                 {
                     layer = new RenderLayer(context, scene.Size, scene.Scaling, src.LayerRoot);
                     _inner.Add(layer);
@@ -59,7 +59,7 @@ namespace Avalonia.Rendering
             _inner.Clear();
         }
 
-        public bool TryGetValue(IVisual layerRoot, out RenderLayer value)
+        public bool TryGetValue(IVisual layerRoot, [NotNullWhen(true)] out RenderLayer? value)
         {
             return _index.TryGetValue(layerRoot, out value);
         }
diff --git a/src/Avalonia.Visuals/Rendering/RenderLoop.cs b/src/Avalonia.Visuals/Rendering/RenderLoop.cs
index b2a6b0da19..a5d7e15f93 100644
--- a/src/Avalonia.Visuals/Rendering/RenderLoop.cs
+++ b/src/Avalonia.Visuals/Rendering/RenderLoop.cs
@@ -19,7 +19,7 @@ namespace Avalonia.Rendering
         private readonly IDispatcher _dispatcher;
         private List<IRenderLoopTask> _items = new List<IRenderLoopTask>();
         private List<IRenderLoopTask> _itemsCopy = new List<IRenderLoopTask>();
-        private IRenderTimer _timer;
+        private IRenderTimer? _timer;
         private int _inTick;
         private int _inUpdate;
 
@@ -49,19 +49,15 @@ namespace Avalonia.Rendering
         {
             get
             {
-                if (_timer == null)
-                {
-                    _timer = AvaloniaLocator.Current.GetService<IRenderTimer>();
-                }
-
-                return _timer;
+                return _timer ??= AvaloniaLocator.Current.GetService<IRenderTimer>() ??
+                    throw new InvalidOperationException("Cannot locate IRenderTimer.");
             }
         }
 
         /// <inheritdoc/>
         public void Add(IRenderLoopTask i)
         {
-            Contract.Requires<ArgumentNullException>(i != null);
+            _ = i ?? throw new ArgumentNullException(nameof(i));
             Dispatcher.UIThread.VerifyAccess();
 
             lock (_items)
@@ -78,7 +74,7 @@ namespace Avalonia.Rendering
         /// <inheritdoc/>
         public void Remove(IRenderLoopTask i)
         {
-            Contract.Requires<ArgumentNullException>(i != null);
+            _ = i ?? throw new ArgumentNullException(nameof(i));
             Dispatcher.UIThread.VerifyAccess();
             lock (_items)
             {
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/BrushDrawOperation.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/BrushDrawOperation.cs
index c559f05d70..cd3dac699a 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/BrushDrawOperation.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/BrushDrawOperation.cs
@@ -17,6 +17,6 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets a collection of child scenes that are needed to draw visual brushes.
         /// </summary>
-        public abstract IDictionary<IVisual, Scene> ChildScenes { get; }
+        public abstract IDictionary<IVisual, Scene>? ChildScenes { get; }
     }
 }
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/DeferredDrawingContextImpl.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/DeferredDrawingContextImpl.cs
index da1a00504a..688cbd83c8 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/DeferredDrawingContextImpl.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/DeferredDrawingContextImpl.cs
@@ -14,7 +14,7 @@ namespace Avalonia.Rendering.SceneGraph
     internal class DeferredDrawingContextImpl : IDrawingContextImpl, IDrawingContextWithAcrylicLikeSupport
     {
         private readonly ISceneBuilder _sceneBuilder;
-        private VisualNode _node;
+        private VisualNode? _node;
         private int _childIndex;
         private int _drawOperationindex;
 
@@ -48,7 +48,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// </returns>
         public UpdateState BeginUpdate(VisualNode node)
         {
-            Contract.Requires<ArgumentNullException>(node != null);
+            _ = node ?? throw new ArgumentNullException(nameof(node));
 
             if (_node != null)
             {
@@ -93,11 +93,11 @@ namespace Avalonia.Rendering.SceneGraph
         /// </remarks>
         public void TrimChildren()
         {
-            _node.TrimChildren(_childIndex);
+            _node!.TrimChildren(_childIndex);
         }
 
         /// <inheritdoc/>
-        public void DrawGeometry(IBrush brush, IPen pen, IGeometryImpl geometry)
+        public void DrawGeometry(IBrush? brush, IPen? pen, IGeometryImpl geometry)
         {
             var next = NextDrawAs<GeometryNode>();
 
@@ -149,7 +149,7 @@ namespace Avalonia.Rendering.SceneGraph
         }
 
         /// <inheritdoc/>
-        public void DrawRectangle(IBrush brush, IPen pen, RoundedRect rect,
+        public void DrawRectangle(IBrush? brush, IPen? pen, RoundedRect rect,
             BoxShadows boxShadows = default)
         {
             var next = NextDrawAs<RectangleNode>();
@@ -179,7 +179,7 @@ namespace Avalonia.Rendering.SceneGraph
             }
         }
 
-        public void DrawEllipse(IBrush brush, IPen pen, Rect rect)
+        public void DrawEllipse(IBrush? brush, IPen? pen, Rect rect)
         {
             var next = NextDrawAs<EllipseNode>();
 
@@ -259,7 +259,7 @@ namespace Avalonia.Rendering.SceneGraph
 
             if (next == null || !next.Item.Equals(null))
             {
-                Add((new GeometryClipNode()));
+                Add(new GeometryClipNode());
             }
             else
             {
@@ -343,8 +343,11 @@ namespace Avalonia.Rendering.SceneGraph
         }
 
         /// <inheritdoc/>
-        public void PushGeometryClip(IGeometryImpl clip)
+        public void PushGeometryClip(IGeometryImpl? clip)
         {
+            if (clip is null)
+                return;
+
             var next = NextDrawAs<GeometryClipNode>();
 
             if (next == null || !next.Item.Equals(Transform, clip))
@@ -406,7 +409,7 @@ namespace Avalonia.Rendering.SceneGraph
         {
             public UpdateState(
                 DeferredDrawingContextImpl owner,
-                VisualNode node,
+                VisualNode? node,
                 int childIndex,
                 int drawOperationIndex)
             {
@@ -418,9 +421,9 @@ namespace Avalonia.Rendering.SceneGraph
 
             public void Dispose()
             {
-                Owner._node.TrimDrawOperations(Owner._drawOperationindex);
+                Owner._node!.TrimDrawOperations(Owner._drawOperationindex);
 
-                var dirty = Owner.Layers.GetOrAdd(Owner._node.LayerRoot).Dirty;
+                var dirty = Owner.Layers.GetOrAdd(Owner._node.LayerRoot!).Dirty;
 
                 var drawOperations = Owner._node.DrawOperations;
                 var drawOperationsCount = drawOperations.Count;
@@ -436,7 +439,7 @@ namespace Avalonia.Rendering.SceneGraph
             }
 
             public DeferredDrawingContextImpl Owner { get; }
-            public VisualNode Node { get; }
+            public VisualNode? Node { get; }
             public int ChildIndex { get; }
             public int DrawOperationIndex { get; }
         }
@@ -451,7 +454,7 @@ namespace Avalonia.Rendering.SceneGraph
 
         private void Add(IRef<IDrawOperation> node)
         {
-            if (_drawOperationindex < _node.DrawOperations.Count)
+            if (_drawOperationindex < _node!.DrawOperations.Count)
             {
                 _node.ReplaceDrawOperation(_drawOperationindex, node);
             }
@@ -463,12 +466,12 @@ namespace Avalonia.Rendering.SceneGraph
             ++_drawOperationindex;
         }
 
-        private IRef<T> NextDrawAs<T>() where T : class, IDrawOperation
+        private IRef<T>? NextDrawAs<T>() where T : class, IDrawOperation
         {
-            return _drawOperationindex < _node.DrawOperations.Count ? _node.DrawOperations[_drawOperationindex] as IRef<T> : null;
+            return _drawOperationindex < _node!.DrawOperations.Count ? _node.DrawOperations[_drawOperationindex] as IRef<T> : null;
         }
 
-        private IDictionary<IVisual, Scene> CreateChildScene(IBrush brush)
+        private IDictionary<IVisual, Scene>? CreateChildScene(IBrush? brush)
         {
             var visualBrush = brush as VisualBrush;
 
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/EllipseNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/EllipseNode.cs
index a8c5579a4b..504256b932 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/EllipseNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/EllipseNode.cs
@@ -14,10 +14,10 @@ namespace Avalonia.Rendering.SceneGraph
     {
         public EllipseNode(
             Matrix transform, 
-            IBrush brush, 
-            IPen pen, 
+            IBrush? brush, 
+            IPen? pen, 
             Rect rect, 
-            IDictionary<IVisual, Scene> childScenes = null) 
+            IDictionary<IVisual, Scene>? childScenes = null) 
             : base(rect.Inflate(pen?.Thickness ?? 0), transform)
         {
             Transform = transform;
@@ -30,12 +30,12 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the fill brush.
         /// </summary>
-        public IBrush Brush { get; }
+        public IBrush? Brush { get; }
 
         /// <summary>
         /// Gets the stroke pen.
         /// </summary>
-        public ImmutablePen Pen { get; }
+        public ImmutablePen? Pen { get; }
 
         /// <summary>
         /// Gets the transform with which the node will be drawn.
@@ -47,9 +47,9 @@ namespace Avalonia.Rendering.SceneGraph
         /// </summary>
         public Rect Rect { get; }
 
-        public override IDictionary<IVisual, Scene> ChildScenes { get; }
+        public override IDictionary<IVisual, Scene>? ChildScenes { get; }
 
-        public bool Equals(Matrix transform, IBrush brush, IPen pen, Rect rect)
+        public bool Equals(Matrix transform, IBrush? brush, IPen? pen, Rect rect)
         {
             return transform == Transform &&
                    Equals(brush, Brush) &&
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/ExperimentalAcrylicNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/ExperimentalAcrylicNode.cs
index 8bd079d070..59ebcf5109 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/ExperimentalAcrylicNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/ExperimentalAcrylicNode.cs
@@ -23,7 +23,7 @@ namespace Avalonia.Rendering.SceneGraph
             : base(rect.Rect, transform)
         {
             Transform = transform;
-            Material = material?.ToImmutable();
+            Material = material.ToImmutable();
             Rect = rect;
         }
 
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryClipNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryClipNode.cs
index 16092d4cbb..667b66420b 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryClipNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryClipNode.cs
@@ -33,7 +33,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the clip to be pushed or null if the operation represents a pop.
         /// </summary>
-        public IGeometryImpl Clip { get; }
+        public IGeometryImpl? Clip { get; }
 
         /// <summary>
         /// Gets the transform with which the node will be drawn.
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryNode.cs
index 508ca0ad18..7de1035441 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/GeometryNode.cs
@@ -20,10 +20,10 @@ namespace Avalonia.Rendering.SceneGraph
         /// <param name="geometry">The geometry.</param>
         /// <param name="childScenes">Child scenes for drawing visual brushes.</param>
         public GeometryNode(Matrix transform,
-            IBrush brush,
-            IPen pen,
+            IBrush? brush,
+            IPen? pen,
             IGeometryImpl geometry,
-            IDictionary<IVisual, Scene> childScenes = null)
+            IDictionary<IVisual, Scene>? childScenes = null)
             : base(geometry.GetRenderBounds(pen), transform)
         {
             Transform = transform;
@@ -41,12 +41,12 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the fill brush.
         /// </summary>
-        public IBrush Brush { get; }
+        public IBrush? Brush { get; }
 
         /// <summary>
         /// Gets the stroke pen.
         /// </summary>
-        public ImmutablePen Pen { get; }
+        public ImmutablePen? Pen { get; }
 
         /// <summary>
         /// Gets the geometry to draw.
@@ -54,7 +54,7 @@ namespace Avalonia.Rendering.SceneGraph
         public IGeometryImpl Geometry { get; }
 
         /// <inheritdoc/>
-        public override IDictionary<IVisual, Scene> ChildScenes { get; }
+        public override IDictionary<IVisual, Scene>? ChildScenes { get; }
 
         /// <summary>
         /// Determines if this draw operation equals another.
@@ -68,7 +68,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// The properties of the other draw operation are passed in as arguments to prevent
         /// allocation of a not-yet-constructed draw operation object.
         /// </remarks>
-        public bool Equals(Matrix transform, IBrush brush, IPen pen, IGeometryImpl geometry)
+        public bool Equals(Matrix transform, IBrush? brush, IPen? pen, IGeometryImpl geometry)
         {
             return transform == Transform &&
                    Equals(brush, Brush) &&
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/GlyphRunNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/GlyphRunNode.cs
index a6dba1bd32..d6da087120 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/GlyphRunNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/GlyphRunNode.cs
@@ -23,11 +23,11 @@ namespace Avalonia.Rendering.SceneGraph
             Matrix transform,
             IBrush foreground,
             GlyphRun glyphRun,
-            IDictionary<IVisual, Scene> childScenes = null)
+            IDictionary<IVisual, Scene>? childScenes = null)
             : base(new Rect(glyphRun.Size), transform)
         {
             Transform = transform;
-            Foreground = foreground?.ToImmutable();
+            Foreground = foreground.ToImmutable();
             GlyphRun = glyphRun;
             ChildScenes = childScenes;
         }
@@ -48,7 +48,7 @@ namespace Avalonia.Rendering.SceneGraph
         public GlyphRun GlyphRun { get; }
 
         /// <inheritdoc/>
-        public override IDictionary<IVisual, Scene> ChildScenes { get; }
+        public override IDictionary<IVisual, Scene>? ChildScenes { get; }
 
         /// <inheritdoc/>
         public override void Render(IDrawingContextImpl context)
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/IVisualNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/IVisualNode.cs
index 6d12b5bca4..e042236346 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/IVisualNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/IVisualNode.cs
@@ -19,7 +19,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the parent scene graph node.
         /// </summary>
-        IVisualNode Parent { get; }
+        IVisualNode? Parent { get; }
 
         /// <summary>
         /// Gets the transform for the node from global to control coordinates.
@@ -54,7 +54,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the node's clip geometry, if any.
         /// </summary>
-        IGeometryImpl GeometryClip { get; set; }
+        IGeometryImpl? GeometryClip { get; set; }
 
         /// <summary>
         /// Gets a value indicating whether one of the node's ancestors has a geometry clip.
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/LineNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/LineNode.cs
index 3dc6d5f50e..a9e1ce8ed7 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/LineNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/LineNode.cs
@@ -25,11 +25,11 @@ namespace Avalonia.Rendering.SceneGraph
             IPen pen,
             Point p1,
             Point p2,
-            IDictionary<IVisual, Scene> childScenes = null)
+            IDictionary<IVisual, Scene>? childScenes = null)
             : base(LineBoundsHelper.CalculateBounds(p1, p2, pen), transform)
         {
             Transform = transform;
-            Pen = pen?.ToImmutable();
+            Pen = pen.ToImmutable();
             P1 = p1;
             P2 = p2;
             ChildScenes = childScenes;
@@ -56,7 +56,7 @@ namespace Avalonia.Rendering.SceneGraph
         public Point P2 { get; }
 
         /// <inheritdoc/>
-        public override IDictionary<IVisual, Scene> ChildScenes { get; }
+        public override IDictionary<IVisual, Scene>? ChildScenes { get; }
 
         /// <summary>
         /// Determines if this draw operation equals another.
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/OpacityMaskNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/OpacityMaskNode.cs
index b8e7b150ac..4b6e7d2254 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/OpacityMaskNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/OpacityMaskNode.cs
@@ -17,10 +17,10 @@ namespace Avalonia.Rendering.SceneGraph
         /// <param name="mask">The opacity mask to push.</param>
         /// <param name="bounds">The bounds of the mask.</param>
         /// <param name="childScenes">Child scenes for drawing visual brushes.</param>
-        public OpacityMaskNode(IBrush mask, Rect bounds, IDictionary<IVisual, Scene> childScenes = null)
+        public OpacityMaskNode(IBrush mask, Rect bounds, IDictionary<IVisual, Scene>? childScenes = null)
             : base(Rect.Empty, Matrix.Identity)
         {
-            Mask = mask?.ToImmutable();
+            Mask = mask.ToImmutable();
             MaskBounds = bounds;
             ChildScenes = childScenes;
         }
@@ -37,7 +37,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the mask to be pushed or null if the operation represents a pop.
         /// </summary>
-        public IBrush Mask { get; }
+        public IBrush? Mask { get; }
 
         /// <summary>
         /// Gets the bounds of the opacity mask or null if the operation represents a pop.
@@ -45,7 +45,7 @@ namespace Avalonia.Rendering.SceneGraph
         public Rect? MaskBounds { get; }
 
         /// <inheritdoc/>
-        public override IDictionary<IVisual, Scene> ChildScenes { get; }
+        public override IDictionary<IVisual, Scene>? ChildScenes { get; }
 
         /// <inheritdoc/>
         public override bool HitTest(Point p) => false;
@@ -60,14 +60,14 @@ namespace Avalonia.Rendering.SceneGraph
         /// The properties of the other draw operation are passed in as arguments to prevent
         /// allocation of a not-yet-constructed draw operation object.
         /// </remarks>
-        public bool Equals(IBrush mask, Rect? bounds) => Mask == mask && MaskBounds == bounds;
+        public bool Equals(IBrush? mask, Rect? bounds) => Mask == mask && MaskBounds == bounds;
 
         /// <inheritdoc/>
         public override void Render(IDrawingContextImpl context)
         {
             if (Mask != null)
             {
-                context.PushOpacityMask(Mask, MaskBounds.Value);
+                context.PushOpacityMask(Mask, MaskBounds!.Value);
             }
             else
             {
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/RectangleNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/RectangleNode.cs
index 285fbce605..3279c3a549 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/RectangleNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/RectangleNode.cs
@@ -22,11 +22,11 @@ namespace Avalonia.Rendering.SceneGraph
         /// <param name="childScenes">Child scenes for drawing visual brushes.</param>
         public RectangleNode(
             Matrix transform,
-            IBrush brush,
-            IPen pen,
+            IBrush? brush,
+            IPen? pen,
             RoundedRect rect,
             BoxShadows boxShadows,
-            IDictionary<IVisual, Scene> childScenes = null)
+            IDictionary<IVisual, Scene>? childScenes = null)
             : base(boxShadows.TransformBounds(rect.Rect).Inflate((pen?.Thickness ?? 0) / 2), transform)
         {
             Transform = transform;
@@ -45,12 +45,12 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the fill brush.
         /// </summary>
-        public IBrush Brush { get; }
+        public IBrush? Brush { get; }
 
         /// <summary>
         /// Gets the stroke pen.
         /// </summary>
-        public ImmutablePen Pen { get; }
+        public ImmutablePen? Pen { get; }
 
         /// <summary>
         /// Gets the rectangle to draw.
@@ -63,7 +63,7 @@ namespace Avalonia.Rendering.SceneGraph
         public BoxShadows BoxShadows { get; }
 
         /// <inheritdoc/>
-        public override IDictionary<IVisual, Scene> ChildScenes { get; }
+        public override IDictionary<IVisual, Scene>? ChildScenes { get; }
 
         /// <summary>
         /// Determines if this draw operation equals another.
@@ -78,7 +78,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// The properties of the other draw operation are passed in as arguments to prevent
         /// allocation of a not-yet-constructed draw operation object.
         /// </remarks>
-        public bool Equals(Matrix transform, IBrush brush, IPen pen, RoundedRect rect, BoxShadows boxShadows)
+        public bool Equals(Matrix transform, IBrush? brush, IPen? pen, RoundedRect rect, BoxShadows boxShadows)
         {
             return transform == Transform &&
                    Equals(brush, Brush) &&
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs
index d8e5baac97..20c23d7bee 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/Scene.cs
@@ -32,7 +32,7 @@ namespace Avalonia.Rendering.SceneGraph
 
         private Scene(VisualNode root, Dictionary<IVisual, IVisualNode> index, SceneLayers layers, int generation)
         {
-            Contract.Requires<ArgumentNullException>(root != null);
+            _ = root ?? throw new ArgumentNullException(nameof(root));
 
             var renderRoot = root.Visual as IRenderRoot;
 
@@ -76,7 +76,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <param name="node">The node.</param>
         public void Add(IVisualNode node)
         {
-            Contract.Requires<ArgumentNullException>(node != null);
+            _ = node ?? throw new ArgumentNullException(nameof(node));
 
             _index.Add(node.Visual, node);
         }
@@ -115,10 +115,9 @@ namespace Avalonia.Rendering.SceneGraph
         /// <returns>
         /// The node representing the visual or null if it could not be found.
         /// </returns>
-        public IVisualNode FindNode(IVisual visual)
+        public IVisualNode? FindNode(IVisual visual)
         {
-            IVisualNode node;
-            _index.TryGetValue(visual, out node);
+            _index.TryGetValue(visual, out var node);
             return node;
         }
 
@@ -129,7 +128,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <param name="root">The root of the subtree to search.</param>
         /// <param name="filter">A filter. May be null.</param>
         /// <returns>The visuals at the specified point.</returns>
-        public IEnumerable<IVisual> HitTest(Point p, IVisual root, Func<IVisual, bool> filter)
+        public IEnumerable<IVisual> HitTest(Point p, IVisual root, Func<IVisual, bool>? filter)
         {
             var node = FindNode(root);
             return (node != null) ? new HitTestEnumerable(node, filter, p, Root) : Enumerable.Empty<IVisual>();
@@ -142,7 +141,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <param name="root">The root of the subtree to search.</param>
         /// <param name="filter">A filter. May be null.</param>
         /// <returns>The visual at the specified point.</returns>
-        public IVisual HitTestFirst(Point p, IVisual root, Func<IVisual, bool> filter)
+        public IVisual? HitTestFirst(Point p, IVisual root, Func<IVisual, bool>? filter)
         {
             var node = FindNode(root);
             return (node != null) ? HitTestFirst(node, p, filter) : null;
@@ -154,14 +153,14 @@ namespace Avalonia.Rendering.SceneGraph
         /// <param name="node">The node.</param>
         public void Remove(IVisualNode node)
         {
-            Contract.Requires<ArgumentNullException>(node != null);
+            _ = node ?? throw new ArgumentNullException(nameof(node));
 
             _index.Remove(node.Visual);
 
             node.Dispose();
         }
 
-        private VisualNode Clone(VisualNode source, IVisualNode parent, Dictionary<IVisual, IVisualNode> index)
+        private VisualNode Clone(VisualNode source, IVisualNode? parent, Dictionary<IVisual, IVisualNode> index)
         {
             var result = source.Clone(parent);
 
@@ -185,7 +184,7 @@ namespace Avalonia.Rendering.SceneGraph
             return result;
         }
 
-        private IVisual HitTestFirst(IVisualNode root, Point p, Func<IVisual, bool> filter)
+        private IVisual HitTestFirst(IVisualNode root, Point p, Func<IVisual, bool>? filter)
         {
             using var enumerator = new HitTestEnumerator(root, filter, p, Root);
 
@@ -197,11 +196,11 @@ namespace Avalonia.Rendering.SceneGraph
         private class HitTestEnumerable : IEnumerable<IVisual>
         {
             private readonly IVisualNode _root;
-            private readonly Func<IVisual, bool> _filter;
+            private readonly Func<IVisual, bool>? _filter;
             private readonly IVisualNode _sceneRoot;
             private readonly Point _point;
             
-            public HitTestEnumerable(IVisualNode root, Func<IVisual, bool> filter, Point point, IVisualNode sceneRoot)
+            public HitTestEnumerable(IVisualNode root, Func<IVisual, bool>? filter, Point point, IVisualNode sceneRoot)
             {
                 _root = root;
                 _filter = filter;
@@ -223,12 +222,12 @@ namespace Avalonia.Rendering.SceneGraph
         private struct HitTestEnumerator : IEnumerator<IVisual>
         {
             private readonly PooledStack<Entry> _nodeStack;
-            private readonly Func<IVisual, bool> _filter;
+            private readonly Func<IVisual, bool>? _filter;
             private readonly IVisualNode _sceneRoot;
-            private IVisual _current;
+            private IVisual? _current;
             private readonly Point _point;
 
-            public HitTestEnumerator(IVisualNode root, Func<IVisual, bool> filter, Point point, IVisualNode sceneRoot)
+            public HitTestEnumerator(IVisualNode root, Func<IVisual, bool>? filter, Point point, IVisualNode sceneRoot)
             {
                 _nodeStack = new PooledStack<Entry>();
                 _nodeStack.Push(new Entry(root, false, null, true));
@@ -283,7 +282,7 @@ namespace Avalonia.Rendering.SceneGraph
                 throw new NotSupportedException();
             }
 
-            public IVisual Current => _current;
+            public IVisual Current => _current!;
 
             object IEnumerator.Current => Current;
 
@@ -307,7 +306,7 @@ namespace Avalonia.Rendering.SceneGraph
                     if (node.GeometryClip != null)
                     {
                         var controlPoint = _sceneRoot.Visual.TranslatePoint(_point, node.Visual);
-                        clipped = !node.GeometryClip.FillContains(controlPoint.Value);
+                        clipped = !node.GeometryClip.FillContains(controlPoint!.Value);
                     }
 
                     if (!clipped && node.Visual is ICustomHitTest custom)
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs
index b9131c26f4..cb916293ac 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneBuilder.cs
@@ -15,7 +15,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <inheritdoc/>
         public void UpdateAll(Scene scene)
         {
-            Contract.Requires<ArgumentNullException>(scene != null);
+            _ = scene ?? throw new ArgumentNullException(nameof(scene));
             Dispatcher.UIThread.VerifyAccess();
 
             UpdateSize(scene);
@@ -32,8 +32,8 @@ namespace Avalonia.Rendering.SceneGraph
         /// <inheritdoc/>
         public bool Update(Scene scene, IVisual visual)
         {
-            Contract.Requires<ArgumentNullException>(scene != null);
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = scene ?? throw new ArgumentNullException(nameof(scene));
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             Dispatcher.UIThread.VerifyAccess();
 
@@ -42,7 +42,7 @@ namespace Avalonia.Rendering.SceneGraph
                 throw new AvaloniaInternalException("Cannot update the scene for an invisible root visual.");
             }
 
-            var node = (VisualNode)scene.FindNode(visual);
+            var node = (VisualNode?)scene.FindNode(visual);
 
             if (visual == scene.Root.Visual)
             {
@@ -58,7 +58,7 @@ namespace Avalonia.Rendering.SceneGraph
                     // The control has changed parents. Remove the node and recurse into the new parent node.
                     ((VisualNode)node.Parent).RemoveChild(node);
                     Deindex(scene, node);
-                    node = (VisualNode)scene.FindNode(visual.VisualParent);
+                    node = (VisualNode?)scene.FindNode(visual.VisualParent);
                 }
 
                 if (visual.IsVisible)
@@ -101,7 +101,7 @@ namespace Avalonia.Rendering.SceneGraph
                     {
                         // The control has been hidden so remove it from its parent and deindex the
                         // node and its descendents.
-                        ((VisualNode)node.Parent)?.RemoveChild(node);
+                        ((VisualNode?)node.Parent)?.RemoveChild(node);
                         Deindex(scene, node);
                         return true;
                     }
@@ -112,7 +112,7 @@ namespace Avalonia.Rendering.SceneGraph
                 // The control has been removed so remove it from its parent and deindex the
                 // node and its descendents.
                 var trim = FindFirstDeadAncestor(scene, node);
-                ((VisualNode)trim.Parent).RemoveChild(trim);
+                ((VisualNode)trim.Parent!).RemoveChild(trim);
                 Deindex(scene, trim);
                 return true;
             }
@@ -120,24 +120,24 @@ namespace Avalonia.Rendering.SceneGraph
             return false;
         }
 
-        private static VisualNode FindExistingAncestor(Scene scene, IVisual visual)
+        private static VisualNode? FindExistingAncestor(Scene scene, IVisual visual)
         {
             var node = scene.FindNode(visual);
 
             while (node == null && visual.IsVisible)
             {
-                visual = visual.VisualParent;
+                visual = visual.VisualParent!;
                 node = scene.FindNode(visual);
             }
 
-            return visual.IsVisible ? (VisualNode)node : null;
+            return visual.IsVisible ? (VisualNode?)node : null;
         }
 
         private static VisualNode FindFirstDeadAncestor(Scene scene, IVisualNode node)
         {
             var parent = node.Parent;
 
-            while (parent.Visual.VisualRoot == null)
+            while (parent!.Visual.VisualRoot == null)
             {
                 node = parent;
                 parent = node.Parent;
@@ -148,7 +148,7 @@ namespace Avalonia.Rendering.SceneGraph
 
         private static object GetOrCreateChildNode(Scene scene, IVisual child, VisualNode parent)
         {
-            var result = (VisualNode)scene.FindNode(child);
+            var result = (VisualNode?)scene.FindNode(child);
 
             if (result != null && result.Parent != parent)
             {
@@ -173,7 +173,7 @@ namespace Avalonia.Rendering.SceneGraph
             var bounds = new Rect(visual.Bounds.Size);
             var contextImpl = (DeferredDrawingContextImpl)context.PlatformImpl;
 
-            contextImpl.Layers.Find(node.LayerRoot)?.Dirty.Add(node.Bounds);
+            contextImpl.Layers.Find(node.LayerRoot!)?.Dirty.Add(node.Bounds);
 
             if (visual.IsVisible)
             {
@@ -353,7 +353,7 @@ namespace Avalonia.Rendering.SceneGraph
 
             node.SubTreeUpdated = true;
 
-            scene.Layers[node.LayerRoot].Dirty.Add(node.Bounds);
+            scene.Layers[node.LayerRoot!].Dirty.Add(node.Bounds);
 
             node.Visual.TransformedBounds = null;
 
@@ -365,10 +365,10 @@ namespace Avalonia.Rendering.SceneGraph
 
         private static void ClearLayer(Scene scene, VisualNode node)
         {
-            var parent = (VisualNode)node.Parent;
+            var parent = (VisualNode)node.Parent!;
             var oldLayerRoot = node.LayerRoot;
-            var newLayerRoot = parent.LayerRoot;
-            var existingDirtyRects = scene.Layers[node.LayerRoot].Dirty;
+            var newLayerRoot = parent.LayerRoot!;
+            var existingDirtyRects = scene.Layers[node.LayerRoot!].Dirty;
             var newDirtyRects = scene.Layers[newLayerRoot].Dirty;
 
             existingDirtyRects.Coalesce();
@@ -378,16 +378,16 @@ namespace Avalonia.Rendering.SceneGraph
                 newDirtyRects.Add(r);
             }
 
-            var oldLayer = scene.Layers[oldLayerRoot];
+            var oldLayer = scene.Layers[oldLayerRoot!];
             PropagateLayer(node, scene.Layers[newLayerRoot], oldLayer);
             scene.Layers.Remove(oldLayer);
         }
 
         private static void MakeLayer(Scene scene, VisualNode node)
         {
-            var oldLayerRoot = node.LayerRoot;
+            var oldLayerRoot = node.LayerRoot!;
             var layer = scene.Layers.Add(node.Visual);
-            var oldLayer = scene.Layers[oldLayerRoot];
+            var oldLayer = scene.Layers[oldLayerRoot!];
 
             UpdateLayer(node, layer);
             PropagateLayer(node, layer, scene.Layers[oldLayerRoot]);
@@ -433,22 +433,23 @@ namespace Avalonia.Rendering.SceneGraph
         // HACK: Disabled layers because they're broken in current renderer. See #2244.
         private static bool ShouldStartLayer(IVisual visual) => false;
 
-        private static IGeometryImpl CreateLayerGeometryClip(VisualNode node)
+        private static IGeometryImpl? CreateLayerGeometryClip(VisualNode node)
         {
-            IGeometryImpl result = null;
+            IGeometryImpl? result = null;
+            VisualNode? n = node;
 
             for (;;)
             {
-                node = (VisualNode)node.Parent;
+                n = (VisualNode?)n!.Parent;
 
-                if (node == null || (node.GeometryClip == null && !node.HasAncestorGeometryClip))
+                if (n == null || (n.GeometryClip == null && !n.HasAncestorGeometryClip))
                 {
                     break;
                 }
 
-                if (node?.GeometryClip != null)
+                if (n?.GeometryClip != null)
                 {
-                    var transformed = node.GeometryClip.WithTransform(node.Transform);
+                    var transformed = n.GeometryClip.WithTransform(n.Transform);
 
                     result = result == null ? transformed : result.Intersect(transformed);
                 }
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayer.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayer.cs
index 02fae562ef..e9474f6e98 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayer.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayer.cs
@@ -54,7 +54,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets or sets the opacity mask for the layer.
         /// </summary>
-        public IBrush OpacityMask { get; set; }
+        public IBrush? OpacityMask { get; set; }
 
         /// <summary>
         /// Gets or sets the target rectangle for the layer opacity mask.
@@ -64,7 +64,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets the layer's geometry clip.
         /// </summary>
-        public IGeometryImpl GeometryClip { get; set; }
+        public IGeometryImpl? GeometryClip { get; set; }
 
         /// <summary>
         /// Gets the dirty rectangles for the layer.
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs
index 25f7383a1a..16d704e5f6 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/SceneLayers.cs
@@ -80,7 +80,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <returns>The created layer.</returns>
         public SceneLayer Add(IVisual layerRoot)
         {
-            Contract.Requires<ArgumentNullException>(layerRoot != null);
+            _ = layerRoot ?? throw new ArgumentNullException(nameof(layerRoot));
 
             var distance = layerRoot.CalculateDistanceFromAncestor(_root);
             var layer = new SceneLayer(layerRoot, distance);
@@ -117,7 +117,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// </returns>
         public bool Exists(IVisual layerRoot)
         {
-            Contract.Requires<ArgumentNullException>(layerRoot != null);
+            _ = layerRoot ?? throw new ArgumentNullException(nameof(layerRoot));
 
             return _index.ContainsKey(layerRoot);
         }
@@ -127,10 +127,9 @@ namespace Avalonia.Rendering.SceneGraph
         /// </summary>
         /// <param name="layerRoot">The root visual.</param>
         /// <returns>The layer if found, otherwise null.</returns>
-        public SceneLayer Find(IVisual layerRoot)
+        public SceneLayer? Find(IVisual layerRoot)
         {
-            SceneLayer result;
-            _index.TryGetValue(layerRoot, out result);
+            _index.TryGetValue(layerRoot, out var result);
             return result;
         }
 
@@ -141,11 +140,9 @@ namespace Avalonia.Rendering.SceneGraph
         /// <returns>The layer.</returns>
         public SceneLayer GetOrAdd(IVisual layerRoot)
         {
-            Contract.Requires<ArgumentNullException>(layerRoot != null);
+            _ = layerRoot ?? throw new ArgumentNullException(nameof(layerRoot));
 
-            SceneLayer result;
-
-            if (!_index.TryGetValue(layerRoot, out result))
+            if (!_index.TryGetValue(layerRoot, out var result))
             {
                 result = Add(layerRoot);
             }
@@ -160,11 +157,9 @@ namespace Avalonia.Rendering.SceneGraph
         /// <returns>True if a matching layer was removed, otherwise false.</returns>
         public bool Remove(IVisual layerRoot)
         {
-            Contract.Requires<ArgumentNullException>(layerRoot != null);
-
-            SceneLayer layer;
+            _ = layerRoot ?? throw new ArgumentNullException(nameof(layerRoot));
 
-            if (_index.TryGetValue(layerRoot, out layer))
+            if (_index.TryGetValue(layerRoot, out var layer))
             {
                 Remove(layer);
             }
@@ -179,7 +174,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <returns>True if the layer was part of the scene, otherwise false.</returns>
         public bool Remove(SceneLayer layer)
         {
-            Contract.Requires<ArgumentNullException>(layer != null);
+            _ = layer ?? throw new ArgumentNullException(nameof(layer));
 
             _index.Remove(layer.LayerRoot);
             return _inner.Remove(layer);
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/TextNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/TextNode.cs
index 4b6c331023..4a1587fb90 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/TextNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/TextNode.cs
@@ -23,11 +23,11 @@ namespace Avalonia.Rendering.SceneGraph
             IBrush foreground,
             Point origin,
             IFormattedTextImpl text,
-            IDictionary<IVisual, Scene> childScenes = null)
+            IDictionary<IVisual, Scene>? childScenes = null)
             : base(text.Bounds.Translate(origin), transform)
         {
             Transform = transform;
-            Foreground = foreground?.ToImmutable();
+            Foreground = foreground.ToImmutable();
             Origin = origin;
             Text = text;
             ChildScenes = childScenes;
@@ -54,7 +54,7 @@ namespace Avalonia.Rendering.SceneGraph
         public IFormattedTextImpl Text { get; }
 
         /// <inheritdoc/>
-        public override IDictionary<IVisual, Scene> ChildScenes { get; }
+        public override IDictionary<IVisual, Scene>? ChildScenes { get; }
 
         /// <inheritdoc/>
         public override void Render(IDrawingContextImpl context)
diff --git a/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs b/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs
index db6b606b41..8a2f1f5073 100644
--- a/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs
+++ b/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs
@@ -1,7 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Reactive.Disposables;
-using Avalonia.Collections;
 using Avalonia.Media;
 using Avalonia.Platform;
 using Avalonia.Utilities;
@@ -19,9 +19,9 @@ namespace Avalonia.Rendering.SceneGraph
 
         private Rect? _bounds;
         private double _opacity;
-        private List<IVisualNode> _children;
-        private List<IRef<IDrawOperation>> _drawOperations;
-        private IRef<IDisposable> _drawOperationsRefCounter;
+        private List<IVisualNode>? _children;
+        private List<IRef<IDrawOperation>>? _drawOperations;
+        private IRef<IDisposable>? _drawOperationsRefCounter;
         private bool _drawOperationsCloned;
         private Matrix transformRestore;
 
@@ -30,11 +30,9 @@ namespace Avalonia.Rendering.SceneGraph
         /// </summary>
         /// <param name="visual">The visual that this node represents.</param>
         /// <param name="parent">The parent scene graph node, if any.</param>
-        public VisualNode(IVisual visual, IVisualNode parent)
+        public VisualNode(IVisual visual, IVisualNode? parent)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
-
-            Visual = visual;
+            Visual = visual ?? throw new ArgumentNullException(nameof(visual));
             Parent = parent;
             HasAncestorGeometryClip = parent != null && 
                 (parent.HasAncestorGeometryClip || parent.GeometryClip != null);
@@ -44,7 +42,7 @@ namespace Avalonia.Rendering.SceneGraph
         public IVisual Visual { get; }
 
         /// <inheritdoc/>
-        public IVisualNode Parent { get; }
+        public IVisualNode? Parent { get; }
 
         /// <inheritdoc/>
         public CornerRadius ClipToBoundsRadius { get; set; }
@@ -65,7 +63,7 @@ namespace Avalonia.Rendering.SceneGraph
         public bool ClipToBounds { get; set; }
 
         /// <inheritdoc/>
-        public IGeometryImpl GeometryClip { get; set; }
+        public IGeometryImpl? GeometryClip { get; set; }
 
         /// <inheritdoc/>
         public bool HasAncestorGeometryClip { get; }
@@ -87,7 +85,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Gets or sets the opacity mask for the scene graph node.
         /// </summary>
-        public IBrush OpacityMask { get; set; }
+        public IBrush? OpacityMask { get; set; }
 
         /// <summary>
         /// Gets a value indicating whether this node in the scene graph has already
@@ -100,7 +98,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// </summary>
         public bool OpacityChanged { get; private set; }
 
-        public IVisual LayerRoot { get; set; }
+        public IVisual? LayerRoot { get; set; }
 
         /// <inheritdoc/>
         public IReadOnlyList<IVisualNode> Children => _children ?? EmptyChildren;
@@ -259,7 +257,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// </summary>
         /// <param name="parent">The new parent node.</param>
         /// <returns>A cloned node.</returns>
-        public VisualNode Clone(IVisualNode parent)
+        public VisualNode Clone(IVisualNode? parent)
         {
             return new VisualNode(Visual, parent)
             {
@@ -382,6 +380,7 @@ namespace Avalonia.Rendering.SceneGraph
             return result;
         }
 
+        [MemberNotNull(nameof(_children))]
         private void EnsureChildrenCreated(int capacity = 0)
         {
             if (_children == null)
@@ -393,6 +392,7 @@ namespace Avalonia.Rendering.SceneGraph
         /// <summary>
         /// Ensures that this node draw operations have been created and are mutable (in case we are using cloned operations).
         /// </summary>
+        [MemberNotNull(nameof(_drawOperations))]
         private void EnsureDrawOperationsCreated()
         {
             if (_drawOperations == null)
@@ -412,7 +412,7 @@ namespace Avalonia.Rendering.SceneGraph
                     _drawOperations.Add(drawOperation.Clone());
                 }
 
-                _drawOperationsRefCounter.Dispose();
+                _drawOperationsRefCounter?.Dispose();
                 _drawOperationsRefCounter = RefCountable.Create(CreateDisposeDrawOperations(_drawOperations));
                 _drawOperationsCloned = false;
             }
diff --git a/src/Avalonia.Visuals/Rendering/SleepLoopRenderTimer.cs b/src/Avalonia.Visuals/Rendering/SleepLoopRenderTimer.cs
index 9cc94ffac3..86595754e9 100644
--- a/src/Avalonia.Visuals/Rendering/SleepLoopRenderTimer.cs
+++ b/src/Avalonia.Visuals/Rendering/SleepLoopRenderTimer.cs
@@ -6,7 +6,7 @@ namespace Avalonia.Rendering
 {
     public class SleepLoopRenderTimer : IRenderTimer
     {
-        private Action<TimeSpan> _tick;
+        private Action<TimeSpan>? _tick;
         private int _count;
         private readonly object _lock = new object();
         private bool _running;
diff --git a/src/Avalonia.Visuals/Rendering/ZIndexComparer.cs b/src/Avalonia.Visuals/Rendering/ZIndexComparer.cs
index e9700c70a5..4566b905c4 100644
--- a/src/Avalonia.Visuals/Rendering/ZIndexComparer.cs
+++ b/src/Avalonia.Visuals/Rendering/ZIndexComparer.cs
@@ -9,6 +9,6 @@ namespace Avalonia.Rendering
         public static readonly ZIndexComparer Instance = new ZIndexComparer();
         public static readonly Comparison<IVisual> ComparisonInstance = Instance.Compare;
 
-        public int Compare(IVisual x, IVisual y) => (x?.ZIndex ?? 0).CompareTo(y?.ZIndex ?? 0);
+        public int Compare(IVisual? x, IVisual? y) => (x?.ZIndex ?? 0).CompareTo(y?.ZIndex ?? 0);
     }
 }
diff --git a/src/Avalonia.Visuals/RoundedRect.cs b/src/Avalonia.Visuals/RoundedRect.cs
index 3452bc1ff8..7d17d681ef 100644
--- a/src/Avalonia.Visuals/RoundedRect.cs
+++ b/src/Avalonia.Visuals/RoundedRect.cs
@@ -9,7 +9,7 @@ namespace Avalonia
             return Rect.Equals(other.Rect) && RadiiTopLeft.Equals(other.RadiiTopLeft) && RadiiTopRight.Equals(other.RadiiTopRight) && RadiiBottomLeft.Equals(other.RadiiBottomLeft) && RadiiBottomRight.Equals(other.RadiiBottomRight);
         }
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return obj is RoundedRect other && Equals(other);
         }
diff --git a/src/Avalonia.Visuals/Size.cs b/src/Avalonia.Visuals/Size.cs
index 8a805dc6c5..69c3ae7319 100644
--- a/src/Avalonia.Visuals/Size.cs
+++ b/src/Avalonia.Visuals/Size.cs
@@ -226,7 +226,7 @@ namespace Avalonia
         /// <returns>
         /// True if <paramref name="obj"/> is a size that equals the current size.
         /// </returns>
-        public override bool Equals(object obj) => obj is Size other && Equals(other);
+        public override bool Equals(object? obj) => obj is Size other && Equals(other);
 
         /// <summary>
         /// Returns a hash code for a <see cref="Size"/>.
diff --git a/src/Avalonia.Visuals/Thickness.cs b/src/Avalonia.Visuals/Thickness.cs
index 06ebc9bfe7..da3a98088f 100644
--- a/src/Avalonia.Visuals/Thickness.cs
+++ b/src/Avalonia.Visuals/Thickness.cs
@@ -252,7 +252,7 @@ namespace Avalonia
         /// <returns>
         /// True if <paramref name="obj"/> is a size that equals the current size.
         /// </returns>
-        public override bool Equals(object obj) => obj is Thickness other && Equals(other);
+        public override bool Equals(object? obj) => obj is Thickness other && Equals(other);
 
         /// <summary>
         /// Returns a hash code for a <see cref="Thickness"/>.
diff --git a/src/Avalonia.Visuals/Visual.cs b/src/Avalonia.Visuals/Visual.cs
index 322b630e83..324b253a0f 100644
--- a/src/Avalonia.Visuals/Visual.cs
+++ b/src/Avalonia.Visuals/Visual.cs
@@ -377,7 +377,7 @@ namespace Avalonia
             }
         }
 
-        protected override void LogicalChildrenCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+        protected override void LogicalChildrenCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             base.LogicalChildrenCollectionChanged(sender, e);
             VisualRoot?.Renderer?.RecalculateChildren(this);
@@ -572,7 +572,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="sender">The sender.</param>
         /// <param name="e">The event args.</param>
-        private void RenderTransformChanged(object sender, EventArgs e)
+        private void RenderTransformChanged(object? sender, EventArgs e)
         {
             InvalidateVisual();
         }
@@ -593,13 +593,14 @@ namespace Avalonia
 
             if (_visualRoot != null)
             {
-                var e = new VisualTreeAttachmentEventArgs(old, VisualRoot);
+                var e = new VisualTreeAttachmentEventArgs(old!, _visualRoot);
                 OnDetachedFromVisualTreeCore(e);
             }
 
             if (_visualParent is IRenderRoot || _visualParent?.IsAttachedToVisualTree == true)
             {
-                var root = this.FindAncestorOfType<IRenderRoot>();
+                var root = this.FindAncestorOfType<IRenderRoot>() ??
+                    throw new AvaloniaInternalException("Visual is atached to visual tree but root could not be found.");
                 var e = new VisualTreeAttachmentEventArgs(_visualParent, root);
                 OnAttachedToVisualTreeCore(e);
             }
@@ -607,28 +608,28 @@ namespace Avalonia
             OnVisualParentChanged(old, value);
         }
 
-        private void AffectsRenderInvalidated(object sender, EventArgs e) => InvalidateVisual();
+        private void AffectsRenderInvalidated(object? sender, EventArgs e) => InvalidateVisual();
 
         /// <summary>
         /// Called when the <see cref="VisualChildren"/> collection changes.
         /// </summary>
         /// <param name="sender">The sender.</param>
         /// <param name="e">The event args.</param>
-        private void VisualChildrenChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void VisualChildrenChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             switch (e.Action)
             {
                 case NotifyCollectionChangedAction.Add:
-                    SetVisualParent(e.NewItems, this);
+                    SetVisualParent(e.NewItems!, this);
                     break;
 
                 case NotifyCollectionChangedAction.Remove:
-                    SetVisualParent(e.OldItems, null);
+                    SetVisualParent(e.OldItems!, null);
                     break;
 
                 case NotifyCollectionChangedAction.Replace:
-                    SetVisualParent(e.OldItems, null);
-                    SetVisualParent(e.NewItems, this);
+                    SetVisualParent(e.OldItems!, null);
+                    SetVisualParent(e.NewItems!, this);
                     break;
             }
         }
@@ -639,7 +640,7 @@ namespace Avalonia
 
             for (var i = 0; i < count; i++)
             {
-                var visual = (Visual) children[i];
+                var visual = (Visual) children[i]!;
                 
                 visual.SetVisualParent(parent);
             }
diff --git a/src/Avalonia.Visuals/VisualExtensions.cs b/src/Avalonia.Visuals/VisualExtensions.cs
index e6523a1469..ff8a515db3 100644
--- a/src/Avalonia.Visuals/VisualExtensions.cs
+++ b/src/Avalonia.Visuals/VisualExtensions.cs
@@ -16,8 +16,10 @@ namespace Avalonia
         /// <returns>The point in client coordinates.</returns>
         public static Point PointToClient(this IVisual visual, PixelPoint point)
         {
-            var rootPoint = visual.VisualRoot.PointToClient(point);
-            return visual.VisualRoot.TranslatePoint(rootPoint, visual).Value;
+            var root = visual.VisualRoot ??
+                throw new ArgumentException("Control does not belong to a visual tree.", nameof(visual));
+            var rootPoint = root.PointToClient(point);
+            return root.TranslatePoint(rootPoint, visual)!.Value;
         }
 
         /// <summary>
@@ -28,8 +30,10 @@ namespace Avalonia
         /// <returns>The point in screen coordinates.</returns>
         public static PixelPoint PointToScreen(this IVisual visual, Point point)
         {
-            var p = visual.TranslatePoint(point, visual.VisualRoot);
-            return visual.VisualRoot.PointToScreen(p.Value);
+            var root = visual.VisualRoot ??
+                throw new ArgumentException("Control does not belong to a visual tree.", nameof(visual));
+            var p = visual.TranslatePoint(point, root);
+            return visual.VisualRoot.PointToScreen(p!.Value);
         }
 
         /// <summary>
@@ -93,28 +97,29 @@ namespace Avalonia
         private static Matrix GetOffsetFrom(IVisual ancestor, IVisual visual)
         {
             var result = Matrix.Identity;
+            IVisual? v = visual;
 
-            while (visual != ancestor)
+            while (v != ancestor)
             {
-                if (visual.RenderTransform?.Value != null)
+                if (v.RenderTransform?.Value != null)
                 {
-                    var origin = visual.RenderTransformOrigin.ToPixels(visual.Bounds.Size);
+                    var origin = v.RenderTransformOrigin.ToPixels(v.Bounds.Size);
                     var offset = Matrix.CreateTranslation(origin);
-                    var renderTransform = (-offset) * visual.RenderTransform.Value * (offset);
+                    var renderTransform = (-offset) * v.RenderTransform.Value * (offset);
 
                     result *= renderTransform;
                 }
 
-                var topLeft = visual.Bounds.TopLeft;
+                var topLeft = v.Bounds.TopLeft;
 
                 if (topLeft != default)
                 {
                     result *= Matrix.CreateTranslation(topLeft);
                 }
 
-                visual = visual.VisualParent;
+                v = v.VisualParent;
 
-                if (visual == null)
+                if (v == null)
                 {
                     throw new ArgumentException("'visual' is not a descendant of 'ancestor'.");
                 }
diff --git a/src/Avalonia.Visuals/VisualTree/TransformedBounds.cs b/src/Avalonia.Visuals/VisualTree/TransformedBounds.cs
index 3aa0392496..42f93d8edb 100644
--- a/src/Avalonia.Visuals/VisualTree/TransformedBounds.cs
+++ b/src/Avalonia.Visuals/VisualTree/TransformedBounds.cs
@@ -54,7 +54,7 @@ namespace Avalonia.VisualTree
             return Bounds == other.Bounds && Clip == other.Clip && Transform == other.Transform;
         }
 
-        public override bool Equals(object obj) => obj is TransformedBounds other && Equals(other);
+        public override bool Equals(object? obj) => obj is TransformedBounds other && Equals(other);
 
         public override int GetHashCode()
         {
diff --git a/src/Avalonia.Visuals/VisualTree/VisualExtensions.cs b/src/Avalonia.Visuals/VisualTree/VisualExtensions.cs
index 8c4004efdc..128a39c082 100644
--- a/src/Avalonia.Visuals/VisualTree/VisualExtensions.cs
+++ b/src/Avalonia.Visuals/VisualTree/VisualExtensions.cs
@@ -19,20 +19,19 @@ namespace Avalonia.VisualTree
         /// The number of steps from the visual to the ancestor or -1 if
         /// <paramref name="visual"/> is not a descendent of <paramref name="ancestor"/>.
         /// </returns>
-        public static int CalculateDistanceFromAncestor(this IVisual visual, IVisual ancestor)
+        public static int CalculateDistanceFromAncestor(this IVisual visual, IVisual? ancestor)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
-
+            IVisual? v = visual ?? throw new ArgumentNullException(nameof(visual));
             var result = 0;
 
-            while (visual != null && visual != ancestor)
+            while (v != null && v != ancestor)
             {
-                visual = visual.VisualParent;
+                v = v.VisualParent;
 
                 result++;
             }
 
-            return visual != null ? result : -1;
+            return v != null ? result : -1;
         }
 
         /// <summary>
@@ -44,15 +43,14 @@ namespace Avalonia.VisualTree
         /// </returns>
         public static int CalculateDistanceFromRoot(IVisual visual)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
-
+            IVisual? v = visual ?? throw new ArgumentNullException(nameof(visual));
             var result = 0;
 
-            visual = visual?.VisualParent;
+            v = v?.VisualParent;
 
-            while (visual != null)
+            while (v != null)
             {
-                visual = visual.VisualParent;
+                v = v.VisualParent;
 
                 result++;
             }
@@ -66,54 +64,56 @@ namespace Avalonia.VisualTree
         /// <param name="visual">The first visual.</param>
         /// <param name="target">The second visual.</param>
         /// <returns>The common ancestor, or null if not found.</returns>
-        public static IVisual FindCommonVisualAncestor(this IVisual visual, IVisual target)
+        public static IVisual? FindCommonVisualAncestor(this IVisual visual, IVisual target)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            IVisual? v = visual ?? throw new ArgumentNullException(nameof(visual));
 
             if (target is null)
             {
                 return null;
             }
 
-            void GoUpwards(ref IVisual node, int count)
+            IVisual? t = target;
+
+            void GoUpwards(ref IVisual? node, int count)
             {
                 for (int i = 0; i < count; ++i)
                 {
-                    node = node.VisualParent;
+                    node = node?.VisualParent;
                 }
             }
 
             // We want to find lowest node first, then make sure that both nodes are at the same height.
             // By doing that we can sometimes find out that other node is our lowest common ancestor.
-            var firstHeight = CalculateDistanceFromRoot(visual);
-            var secondHeight = CalculateDistanceFromRoot(target);
+            var firstHeight = CalculateDistanceFromRoot(v);
+            var secondHeight = CalculateDistanceFromRoot(t);
 
             if (firstHeight > secondHeight)
             {
-                GoUpwards(ref visual, firstHeight - secondHeight);
+                GoUpwards(ref v, firstHeight - secondHeight);
             }
             else
             {
-                GoUpwards(ref target, secondHeight - firstHeight);
+                GoUpwards(ref t, secondHeight - firstHeight);
             }
 
-            if (visual == target)
+            if (v == t)
             {
-                return visual;
+                return v;
             }
 
-            while (visual != null && target != null)
+            while (v != null && t != null)
             {
-                IVisual firstParent = visual.VisualParent;
-                IVisual secondParent = target.VisualParent;
+                IVisual? firstParent = v.VisualParent;
+                IVisual? secondParent = t.VisualParent;
 
                 if (firstParent == secondParent)
                 {
                     return firstParent;
                 }
 
-                visual = visual.VisualParent;
-                target = target.VisualParent;
+                v = v.VisualParent;
+                t = t.VisualParent;
             }
 
             return null;
@@ -126,14 +126,14 @@ namespace Avalonia.VisualTree
         /// <returns>The visual's ancestors.</returns>
         public static IEnumerable<IVisual> GetVisualAncestors(this IVisual visual)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            IVisual? v = visual ?? throw new ArgumentNullException(nameof(visual));
 
-            visual = visual.VisualParent;
+            v = v.VisualParent;
 
-            while (visual != null)
+            while (v != null)
             {
-                yield return visual;
-                visual = visual.VisualParent;
+                yield return v;
+                v = v.VisualParent;
             }
         }
 
@@ -144,14 +144,14 @@ namespace Avalonia.VisualTree
         /// <param name="visual">The visual.</param>
         /// <param name="includeSelf">If given visual should be included in search.</param>
         /// <returns>First ancestor of given type.</returns>
-        public static T FindAncestorOfType<T>(this IVisual visual, bool includeSelf = false) where T : class
+        public static T? FindAncestorOfType<T>(this IVisual visual, bool includeSelf = false) where T : class
         {
             if (visual is null)
             {
                 return null;
             }
 
-            IVisual parent = includeSelf ? visual : visual.VisualParent;
+            IVisual? parent = includeSelf ? visual : visual.VisualParent;
 
             while (parent != null)
             {
@@ -173,7 +173,7 @@ namespace Avalonia.VisualTree
         /// <param name="visual">The visual.</param>
         /// <param name="includeSelf">If given visual should be included in search.</param>
         /// <returns>First descendant of given type.</returns>
-        public static T FindDescendantOfType<T>(this IVisual visual, bool includeSelf = false) where T : class
+        public static T? FindDescendantOfType<T>(this IVisual visual, bool includeSelf = false) where T : class
         {
             if (visual is null)
             {
@@ -195,7 +195,7 @@ namespace Avalonia.VisualTree
         /// <returns>The visual and its ancestors.</returns>
         public static IEnumerable<IVisual> GetSelfAndVisualAncestors(this IVisual visual)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             yield return visual;
 
@@ -211,9 +211,9 @@ namespace Avalonia.VisualTree
         /// <param name="visual">The root visual to test.</param>
         /// <param name="p">The point.</param>
         /// <returns>The visual at the requested point.</returns>
-        public static IVisual GetVisualAt(this IVisual visual, Point p)
+        public static IVisual? GetVisualAt(this IVisual visual, Point p)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             return visual.GetVisualAt(p, x => x.IsVisible);
         }
@@ -228,11 +228,17 @@ namespace Avalonia.VisualTree
         /// children will be excluded from the results.
         /// </param>
         /// <returns>The visual at the requested point.</returns>
-        public static IVisual GetVisualAt(this IVisual visual, Point p, Func<IVisual, bool> filter)
+        public static IVisual? GetVisualAt(this IVisual visual, Point p, Func<IVisual, bool> filter)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             var root = visual.GetVisualRoot();
+
+            if (root is null)
+            {
+                return null;
+            }
+
             var rootPoint = visual.TranslatePoint(p, root);
 
             if (rootPoint.HasValue)
@@ -253,7 +259,7 @@ namespace Avalonia.VisualTree
             this IVisual visual,
             Point p)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             return visual.GetVisualsAt(p, x => x.IsVisible);
         }
@@ -273,9 +279,15 @@ namespace Avalonia.VisualTree
             Point p,
             Func<IVisual, bool> filter)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             var root = visual.GetVisualRoot();
+
+            if (root is null)
+            {
+                return Array.Empty<IVisual>();
+            }
+
             var rootPoint = visual.TranslatePoint(p, root);
 
             if (rootPoint.HasValue)
@@ -334,7 +346,7 @@ namespace Avalonia.VisualTree
         /// </summary>
         /// <param name="visual">The visual.</param>
         /// <returns>The parent, or null if the visual is unparented.</returns>
-        public static IVisual GetVisualParent(this IVisual visual)
+        public static IVisual? GetVisualParent(this IVisual visual)
         {
             return visual.VisualParent;
         }
@@ -347,7 +359,7 @@ namespace Avalonia.VisualTree
         /// <returns>
         /// The parent, or null if the visual is unparented or its parent is not of type <typeparamref name="T"/>.
         /// </returns>
-        public static T GetVisualParent<T>(this IVisual visual) where T : class
+        public static T? GetVisualParent<T>(this IVisual visual) where T : class
         {
             return visual.VisualParent as T;
         }
@@ -359,9 +371,9 @@ namespace Avalonia.VisualTree
         /// <returns>
         /// The root visual or null if the visual is not rooted.
         /// </returns>
-        public static IRenderRoot GetVisualRoot(this IVisual visual)
+        public static IRenderRoot? GetVisualRoot(this IVisual visual)
         {
-            Contract.Requires<ArgumentNullException>(visual != null);
+            _ = visual ?? throw new ArgumentNullException(nameof(visual));
 
             return visual as IRenderRoot ?? visual.VisualRoot;
         }
@@ -377,7 +389,7 @@ namespace Avalonia.VisualTree
         /// </returns>
         public static bool IsVisualAncestorOf(this IVisual visual, IVisual target)
         {
-            IVisual current = target?.VisualParent;
+            IVisual? current = target?.VisualParent;
 
             while (current != null)
             {
@@ -402,10 +414,10 @@ namespace Avalonia.VisualTree
                     ZIndex = element.ZIndex,
                 })
                 .OrderBy(x => x, null)
-                .Select(x => x.Element);
+                .Select(x => x.Element!);
         }
 
-        private static T FindDescendantOfTypeCore<T>(IVisual visual) where T : class
+        private static T? FindDescendantOfTypeCore<T>(IVisual visual) where T : class
         {
             var visualChildren = visual.VisualChildren;
             var visualChildrenCount = visualChildren.Count;
@@ -432,12 +444,15 @@ namespace Avalonia.VisualTree
 
         private class ZOrderElement : IComparable<ZOrderElement>
         {
-            public IVisual Element { get; set; }
+            public IVisual? Element { get; set; }
             public int Index { get; set; }
             public int ZIndex { get; set; }
 
-            public int CompareTo(ZOrderElement other)
+            public int CompareTo(ZOrderElement? other)
             {
+                if (other is null)
+                    return 1;
+
                 var z = other.ZIndex - ZIndex;
 
                 if (z != 0)
diff --git a/src/Avalonia.Visuals/VisualTree/VisualLocator.cs b/src/Avalonia.Visuals/VisualTree/VisualLocator.cs
index 1e0662c17a..940c87bafa 100644
--- a/src/Avalonia.Visuals/VisualTree/VisualLocator.cs
+++ b/src/Avalonia.Visuals/VisualTree/VisualLocator.cs
@@ -6,18 +6,18 @@ namespace Avalonia.VisualTree
 {
     public class VisualLocator
     {
-        public static IObservable<IVisual> Track(IVisual relativeTo, int ancestorLevel, Type ancestorType = null)
+        public static IObservable<IVisual?> Track(IVisual relativeTo, int ancestorLevel, Type? ancestorType = null)
         {
             return new VisualTracker(relativeTo, ancestorLevel, ancestorType);
         }
 
-        private class VisualTracker : LightweightObservableBase<IVisual>
+        private class VisualTracker : LightweightObservableBase<IVisual?>
         {
             private readonly IVisual _relativeTo;
             private readonly int _ancestorLevel;
-            private readonly Type _ancestorType;
+            private readonly Type? _ancestorType;
 
-            public VisualTracker(IVisual relativeTo, int ancestorLevel, Type ancestorType)
+            public VisualTracker(IVisual relativeTo, int ancestorLevel, Type? ancestorType)
             {
                 _relativeTo = relativeTo;
                 _ancestorLevel = ancestorLevel;
@@ -36,14 +36,14 @@ namespace Avalonia.VisualTree
                 _relativeTo.DetachedFromVisualTree -= AttachedDetached;
             }
 
-            protected override void Subscribed(IObserver<IVisual> observer, bool first)
+            protected override void Subscribed(IObserver<IVisual?> observer, bool first)
             {
                 observer.OnNext(GetResult());
             }
 
-            private void AttachedDetached(object sender, VisualTreeAttachmentEventArgs e) => PublishNext(GetResult());
+            private void AttachedDetached(object? sender, VisualTreeAttachmentEventArgs e) => PublishNext(GetResult());
 
-            private IVisual GetResult()
+            private IVisual? GetResult()
             {
                 if (_relativeTo.IsAttachedToVisualTree)
                 {
diff --git a/src/Avalonia.Visuals/VisualTreeAttachmentEventArgs.cs b/src/Avalonia.Visuals/VisualTreeAttachmentEventArgs.cs
index d8f6ea8296..57a9340be8 100644
--- a/src/Avalonia.Visuals/VisualTreeAttachmentEventArgs.cs
+++ b/src/Avalonia.Visuals/VisualTreeAttachmentEventArgs.cs
@@ -17,11 +17,8 @@ namespace Avalonia
         /// <param name="root">The root visual.</param>
         public VisualTreeAttachmentEventArgs(IVisual parent, IRenderRoot root)
         {
-            Contract.Requires<ArgumentNullException>(parent != null);
-            Contract.Requires<ArgumentNullException>(root != null);
-
-            Parent = parent;
-            Root = root;
+            Parent = parent ?? throw new ArgumentNullException(nameof(parent));
+            Root = root ?? throw new ArgumentNullException(nameof(root));
         }
 
         /// <summary>
diff --git a/src/Avalonia.X11/Avalonia.X11.csproj b/src/Avalonia.X11/Avalonia.X11.csproj
index f9efe5581f..9ba5c9d15f 100644
--- a/src/Avalonia.X11/Avalonia.X11.csproj
+++ b/src/Avalonia.X11/Avalonia.X11.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
-        <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+        <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
         <PackageId>Avalonia.X11</PackageId>
     </PropertyGroup>
diff --git a/src/Avalonia.X11/X11CursorFactory.cs b/src/Avalonia.X11/X11CursorFactory.cs
index 8e5cac1400..60f035cd7e 100644
--- a/src/Avalonia.X11/X11CursorFactory.cs
+++ b/src/Avalonia.X11/X11CursorFactory.cs
@@ -94,10 +94,8 @@ namespace Avalonia.X11
             {
                 var size = Marshal.SizeOf<XcursorImage>() +
                     (bitmap.PixelSize.Width * bitmap.PixelSize.Height * 4);
-                var runtimePlatform = AvaloniaLocator.Current.GetService<IRuntimePlatform>() ??
-                    throw new InvalidOperationException("Unable to locate IRuntimePlatform");
-                var platformRenderInterface = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>() ??
-                    throw new InvalidOperationException("Unable to locate IPlatformRenderInterface");
+                var runtimePlatform = AvaloniaLocator.Current.GetRequiredService<IRuntimePlatform>();
+                var platformRenderInterface = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
 
                 _pixelSize = bitmap.PixelSize;
                 _blob = runtimePlatform.AllocBlob(size);
diff --git a/src/Avalonia.X11/X11Window.cs b/src/Avalonia.X11/X11Window.cs
index 982bca6439..211a8e4f79 100644
--- a/src/Avalonia.X11/X11Window.cs
+++ b/src/Avalonia.X11/X11Window.cs
@@ -1157,7 +1157,7 @@ namespace Avalonia.X11
         public ITextInputMethodImpl TextInputMethod => _ime;
 
         public void SetTransparencyLevelHint(WindowTransparencyLevel transparencyLevel) =>
-            _transparencyHelper.SetTransparencyRequest(transparencyLevel);
+            _transparencyHelper?.SetTransparencyRequest(transparencyLevel);
 
         public void SetWindowManagerAddShadowHint(bool enabled)
         {
diff --git a/src/Linux/Avalonia.LinuxFramebuffer/Avalonia.LinuxFramebuffer.csproj b/src/Linux/Avalonia.LinuxFramebuffer/Avalonia.LinuxFramebuffer.csproj
index 41e3049bb8..6a2eb18385 100644
--- a/src/Linux/Avalonia.LinuxFramebuffer/Avalonia.LinuxFramebuffer.csproj
+++ b/src/Linux/Avalonia.LinuxFramebuffer/Avalonia.LinuxFramebuffer.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <PackageId>Avalonia.LinuxFramebuffer</PackageId>
   </PropertyGroup>
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/Avalonia.Markup.Xaml.Loader.csproj b/src/Markup/Avalonia.Markup.Xaml.Loader/Avalonia.Markup.Xaml.Loader.csproj
index fdfb99789e..f75c96c759 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/Avalonia.Markup.Xaml.Loader.csproj
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/Avalonia.Markup.Xaml.Loader.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <IsPackable>true</IsPackable>
     <PackageId>Avalonia.Markup.Xaml.Loader</PackageId>
     <DefineConstants>$(DefineConstants);XAMLX_INTERNAL</DefineConstants>
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathTransformer.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathTransformer.cs
index 4d8c940bbc..048a6220c5 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathTransformer.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPathTransformer.cs
@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using XamlX.Ast;
 using XamlX.Transform;
+using XamlX.Transform.Transformers;
 using XamlX.TypeSystem;
 
 namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
@@ -15,7 +16,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             {
                 IXamlType startType = null;
                 var sourceProperty = binding.Children.OfType<XamlPropertyAssignmentNode>().FirstOrDefault(c => c.Property.Name == "Source");
-                if ((sourceProperty?.Values.Count ?? 0) == 1)
+                var dataTypeProperty = binding.Children.OfType<XamlPropertyAssignmentNode>().FirstOrDefault(c => c.Property.Name == "DataType");
+                if (sourceProperty?.Values.Count is 1)
                 {
                     var sourceValue = sourceProperty.Values[0];
                     switch (sourceValue)
@@ -99,7 +101,12 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     }
                 }
 
-                if (startType == null)
+                if (dataTypeProperty?.Values.Count is 1 && dataTypeProperty.Values[0] is XamlAstTextNode text)
+                {
+                    startType = TypeReferenceResolver.ResolveType(context, text.Text, isMarkupExtension: false, text, strict: true).Type;
+                }
+
+                Func<IXamlType> startTypeResolver = startType is not null ? () => startType : () =>
                 {
                     var parentDataContextNode = context.ParentNodes().OfType<AvaloniaXamlIlDataContextTypeMetadataNode>().FirstOrDefault();
                     if (parentDataContextNode is null)
@@ -107,10 +114,10 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                         throw new XamlX.XamlParseException("Cannot parse a compiled binding without an explicit x:DataType directive to give a starting data type for bindings.", binding);
                     }
 
-                    startType = parentDataContextNode.DataContextType;
-                }
+                    return parentDataContextNode.DataContextType;
+                };
 
-                XamlIlBindingPathHelper.UpdateCompiledBindingExtension(context, binding, startType);
+                XamlIlBindingPathHelper.UpdateCompiledBindingExtension(context, binding, startTypeResolver, context.ParentNodes().OfType<XamlAstConstructableObjectNode>().First().Type.GetClrType());
             }
 
             return node;
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlDataContextTypeTransformer.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlDataContextTypeTransformer.cs
index 349143253e..cf691db860 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlDataContextTypeTransformer.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlDataContextTypeTransformer.cs
@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using XamlX;
@@ -11,7 +12,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 {
     class AvaloniaXamlIlDataContextTypeTransformer : IXamlAstTransformer
     {
-        private const string AvaloniaNs = "https://github.com/avaloniaui";
         public IXamlAstNode Transform(AstTransformationContext context, IXamlAstNode node)
         {
             if (context.ParentNodes().FirstOrDefault() is AvaloniaXamlIlDataContextTypeMetadataNode)
@@ -120,7 +120,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                     var parentItemsDataContext = context.ParentNodes().SkipWhile(n => n != parentObject).OfType<AvaloniaXamlIlDataContextTypeMetadataNode>().FirstOrDefault();
                     if (parentItemsDataContext != null)
                     {
-                        itemsCollectionType = XamlIlBindingPathHelper.UpdateCompiledBindingExtension(context, parentItemsBinding, parentItemsDataContext.DataContextType);
+                        itemsCollectionType = XamlIlBindingPathHelper.UpdateCompiledBindingExtension(context, parentItemsBinding, () => parentItemsDataContext.DataContextType, parentObject.Type.GetClrType());
                     }
                 }
             }
@@ -153,16 +153,24 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             }
             else if (obj.Type.GetClrType().Equals(context.GetAvaloniaTypes().CompiledBindingExtension))
             {
-                IXamlType startType;
-                var parentDataContextNode = context.ParentNodes().OfType<AvaloniaXamlIlDataContextTypeMetadataNode>().FirstOrDefault();
-                if (parentDataContextNode is null)
+                Func<IXamlType> startTypeResolver = () =>
                 {
-                    throw new XamlX.XamlParseException("Cannot parse a compiled binding without an explicit x:DataType directive to give a starting data type for bindings.", obj);
-                }
+                    var dataTypeProperty = obj.Children.OfType<XamlPropertyAssignmentNode>().FirstOrDefault(c => c.Property.Name == "DataType");
+                    if (dataTypeProperty?.Values.Count is 1 && dataTypeProperty.Values[0] is XamlAstTextNode text)
+                    {
+                        return TypeReferenceResolver.ResolveType(context, text.Text, isMarkupExtension: false, text, strict: true).Type;
+                    }
+
+                    var parentDataContextNode = context.ParentNodes().OfType<AvaloniaXamlIlDataContextTypeMetadataNode>().FirstOrDefault();
+                    if (parentDataContextNode is null)
+                    {
+                        throw new XamlX.XamlParseException("Cannot parse a compiled binding without an explicit x:DataType directive to give a starting data type for bindings.", obj);
+                    }
 
-                startType = parentDataContextNode.DataContextType;
+                    return parentDataContextNode.DataContextType;
+                };
 
-                var bindingResultType = XamlIlBindingPathHelper.UpdateCompiledBindingExtension(context, obj, startType);
+                var bindingResultType = XamlIlBindingPathHelper.UpdateCompiledBindingExtension(context, obj, startTypeResolver, on.Type.GetClrType());
                 return new AvaloniaXamlIlDataContextTypeMetadataNode(on, bindingResultType);
             }
 
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlSelectorTransformer.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlSelectorTransformer.cs
index dfabd66d17..79589a5a4f 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlSelectorTransformer.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlSelectorTransformer.cs
@@ -40,6 +40,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
 
             var selectorType = pn.Property.GetClrProperty().Getter.ReturnType;
             var initialNode = new XamlIlSelectorInitialNode(node, selectorType);
+            var avaloniaAttachedPropertyT = context.GetAvaloniaTypes().AvaloniaAttachedPropertyT;
             XamlIlSelectorNode Create(IEnumerable<SelectorGrammar.ISyntax> syntax,
                 Func<string, string, XamlAstClrTypeReference> typeResolver)
             {
@@ -85,6 +86,47 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                             result = new XamlIlPropertyEqualsSelector(result, targetProperty, typedValue);
                             break;
                         }
+                        case SelectorGrammar.AttachedPropertySyntax attachedProperty:
+                            {
+                                var targetType = result?.TargetType;
+                                if (targetType == null)
+                                {
+                                    throw new XamlParseException("Attached Property selectors must be applied to a type.",node);
+                                }
+                                var attachedPropertyOwnerType = typeResolver(attachedProperty.Xmlns, attachedProperty.TypeName).Type;
+
+                                if (attachedPropertyOwnerType is null)
+                                {
+                                    throw new XamlParseException($"Cannot find '{attachedProperty.Xmlns}:{attachedProperty.TypeName}",node);
+                                }
+
+                                var attachedPropertyName = attachedProperty.Property + "Property";
+
+                                var targetPropertyField = attachedPropertyOwnerType.GetAllFields()
+                                    .FirstOrDefault(f => f.IsStatic
+                                        && f.IsPublic
+                                        && f.Name == attachedPropertyName
+                                        && f.FieldType.GenericTypeDefinition == avaloniaAttachedPropertyT
+                                        );
+
+                                if (targetPropertyField is null)
+                                {
+                                    throw new XamlParseException($"Cannot find '{attachedProperty.Property}' on '{attachedPropertyOwnerType.GetFqn()}", node);
+                                }
+
+                                var targetPropertyType = XamlIlAvaloniaPropertyHelper
+                                    .GetAvaloniaPropertyType(targetPropertyField, context.GetAvaloniaTypes(), node);
+
+                                if (!XamlTransformHelpers.TryGetCorrectlyTypedValue(context,
+                                    new XamlAstTextNode(node, attachedProperty.Value, context.Configuration.WellKnownTypes.String),
+                                    targetPropertyType, out var typedValue))
+                                        throw new XamlParseException(
+                                            $"Cannot convert '{attachedProperty.Value}' to '{targetPropertyType.GetFqn()}",
+                                            node);
+
+                                result = new XamlIlAttacchedPropertyEqualsSelector(result, targetPropertyField, typedValue);
+                                break;
+                            }
                         case SelectorGrammar.ChildSyntax child:
                             result = new XamlIlCombinatorSelector(result, XamlIlCombinatorSelector.SelectorType.Child);
                             break;
@@ -338,6 +380,34 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         }
     }
 
+
+    class XamlIlAttacchedPropertyEqualsSelector : XamlIlSelectorNode
+    {
+        public XamlIlAttacchedPropertyEqualsSelector(XamlIlSelectorNode previous,
+            IXamlField propertyFiled,
+            IXamlAstValueNode value)
+            : base(previous)
+        {
+            PropertyFiled = propertyFiled;
+            Value = value;
+        }
+
+        public IXamlField PropertyFiled { get; set; }
+        public IXamlAstValueNode Value { get; set; }
+
+        public override IXamlType TargetType => Previous?.TargetType;
+        protected override void DoEmit(XamlEmitContext<IXamlILEmitter, XamlILNodeEmitResult> context, IXamlILEmitter codeGen)
+        {
+            codeGen.Ldsfld(PropertyFiled);
+            context.Emit(Value, codeGen, context.Configuration.WellKnownTypes.Object);
+            EmitCall(context, codeGen,
+                m => m.Name == "PropertyEquals"
+                     && m.Parameters.Count == 3
+                     && m.Parameters[1].FullName == "Avalonia.AvaloniaProperty"
+                     && m.Parameters[2].Equals(context.Configuration.WellKnownTypes.Object));
+        }
+    }
+
     class XamlIlOrSelectorNode : XamlIlSelectorNode
     {
         List<XamlIlSelectorNode> _selectors = new List<XamlIlSelectorNode>();
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
index 6dd3521183..89b88790dc 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs
@@ -15,6 +15,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType AvaloniaObjectExtensions { get; }
         public IXamlType AvaloniaProperty { get; }
         public IXamlType AvaloniaPropertyT { get; }
+        public IXamlType AvaloniaAttachedPropertyT { get; }
         public IXamlType IBinding { get; }
         public IXamlMethod AvaloniaObjectBindMethod { get; }
         public IXamlMethod AvaloniaObjectSetValueMethod { get; }
@@ -93,6 +94,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             AvaloniaObjectExtensions = cfg.TypeSystem.GetType("Avalonia.AvaloniaObjectExtensions");
             AvaloniaProperty = cfg.TypeSystem.GetType("Avalonia.AvaloniaProperty");
             AvaloniaPropertyT = cfg.TypeSystem.GetType("Avalonia.AvaloniaProperty`1");
+            AvaloniaAttachedPropertyT = cfg.TypeSystem.GetType("Avalonia.AttachedProperty`1");
             BindingPriority = cfg.TypeSystem.GetType("Avalonia.Data.BindingPriority");
             IBinding = cfg.TypeSystem.GetType("Avalonia.Data.IBinding");
             IDisposable = cfg.TypeSystem.GetType("System.IDisposable");
diff --git a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlBindingPathHelper.cs b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlBindingPathHelper.cs
index 1974dfe3bc..7f7f60ed94 100644
--- a/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlBindingPathHelper.cs
+++ b/src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/XamlIlBindingPathHelper.cs
@@ -20,7 +20,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 {
     static class XamlIlBindingPathHelper
     {
-        public static IXamlType UpdateCompiledBindingExtension(AstTransformationContext context, XamlAstConstructableObjectNode binding, IXamlType startType)
+        public static IXamlType UpdateCompiledBindingExtension(AstTransformationContext context, XamlAstConstructableObjectNode binding, Func<IXamlType> startTypeResolver, IXamlType selfType)
         {
             IXamlType bindingResultType = null;
             if (binding.Arguments.Count > 0 && binding.Arguments[0] is ParsedBindingPathNode bindingPath)
@@ -28,7 +28,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 var transformed = TransformBindingPath(
                     context,
                     bindingPath,
-                    startType,
+                    startTypeResolver,
+                    selfType,
                     bindingPath.Path);
 
                 bindingResultType = transformed.BindingResultType;
@@ -41,7 +42,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
 
                 if (bindingPathAssignment is null)
                 {
-                    return startType;
+                    return startTypeResolver();
                 }
 
                 if (bindingPathAssignment.Values[0] is ParsedBindingPathNode bindingPathNode)
@@ -49,7 +50,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                     var transformed = TransformBindingPath(
                         context,
                         bindingPathNode,
-                        startType,
+                        startTypeResolver,
+                        selfType,
                         bindingPathNode.Path);
 
                     bindingResultType = transformed.BindingResultType;
@@ -64,13 +66,13 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
             return bindingResultType;
         }
 
-        private static IXamlIlBindingPathNode TransformBindingPath(AstTransformationContext context, IXamlLineInfo lineInfo, IXamlType startType, IEnumerable<BindingExpressionGrammar.INode> bindingExpression)
+        private static IXamlIlBindingPathNode TransformBindingPath(AstTransformationContext context, IXamlLineInfo lineInfo, Func<IXamlType> startTypeResolver, IXamlType selfType, IEnumerable<BindingExpressionGrammar.INode> bindingExpression)
         {
             List<IXamlIlBindingPathElementNode> transformNodes = new List<IXamlIlBindingPathElementNode>();
             List<IXamlIlBindingPathElementNode> nodes = new List<IXamlIlBindingPathElementNode>();
             foreach (var astNode in bindingExpression)
             {
-                var targetType = nodes.Count == 0 ? startType : nodes[nodes.Count - 1].Type;
+                var targetTypeResolver = nodes.Count == 0 ? startTypeResolver : () => nodes[nodes.Count - 1].Type;
                 switch (astNode)
                 {
                     case BindingExpressionGrammar.EmptyExpressionNode _:
@@ -79,59 +81,66 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                         transformNodes.Add(new XamlIlNotPathElementNode(context.Configuration.WellKnownTypes.Boolean));
                         break;
                     case BindingExpressionGrammar.StreamNode _:
-                        IXamlType observableType;
-                        if (targetType.GenericTypeDefinition?.Equals(context.Configuration.TypeSystem.FindType("System.IObservable`1")) == true)
                         {
-                            observableType = targetType;
-                        }
-                        else
-                        {
-                            observableType = targetType.GetAllInterfaces().FirstOrDefault(i => i.GenericTypeDefinition?.Equals(context.Configuration.TypeSystem.FindType("System.IObservable`1")) ?? false);
-                        }
+                            IXamlType targetType = targetTypeResolver();
+                            IXamlType observableType;
+                            if (targetType.GenericTypeDefinition?.Equals(context.Configuration.TypeSystem.FindType("System.IObservable`1")) == true)
+                            {
+                                observableType = targetType;
+                            }
+                            else
+                            {
+                                observableType = targetType.GetAllInterfaces().FirstOrDefault(i => i.GenericTypeDefinition?.Equals(context.Configuration.TypeSystem.FindType("System.IObservable`1")) ?? false);
+                            }
 
-                        if (observableType != null)
-                        {
-                            nodes.Add(new XamlIlStreamObservablePathElementNode(observableType.GenericArguments[0]));
-                            break;
-                        }
-                        bool foundTask = false;
-                        for (var currentType = targetType; currentType != null; currentType = currentType.BaseType)
-                        {
-                            if (currentType.GenericTypeDefinition.Equals(context.Configuration.TypeSystem.GetType("System.Threading.Tasks.Task`1")))
+                            if (observableType != null)
                             {
-                                foundTask = true;
-                                nodes.Add(new XamlIlStreamTaskPathElementNode(currentType.GenericArguments[0]));
+                                nodes.Add(new XamlIlStreamObservablePathElementNode(observableType.GenericArguments[0]));
                                 break;
                             }
+                            bool foundTask = false;
+                            for (var currentType = targetType; currentType != null; currentType = currentType.BaseType)
+                            {
+                                if (currentType.GenericTypeDefinition.Equals(context.Configuration.TypeSystem.GetType("System.Threading.Tasks.Task`1")))
+                                {
+                                    foundTask = true;
+                                    nodes.Add(new XamlIlStreamTaskPathElementNode(currentType.GenericArguments[0]));
+                                    break;
+                                }
+                            }
+                            if (foundTask)
+                            {
+                                break;
+                            }
+                            throw new XamlX.XamlParseException($"Compiled bindings do not support stream bindings for objects of type {targetType.FullName}.", lineInfo);
                         }
-                        if (foundTask)
-                        {
-                            break;
-                        }
-                        throw new XamlX.XamlParseException($"Compiled bindings do not support stream bindings for objects of type {targetType.FullName}.", lineInfo);
                     case BindingExpressionGrammar.PropertyNameNode propName:
-                        var avaloniaPropertyFieldNameMaybe = propName.PropertyName + "Property";
-                        var avaloniaPropertyFieldMaybe = targetType.GetAllFields().FirstOrDefault(f =>
-                            f.IsStatic && f.IsPublic && f.Name == avaloniaPropertyFieldNameMaybe);
-
-                        if (avaloniaPropertyFieldMaybe != null)
                         {
-                            nodes.Add(new XamlIlAvaloniaPropertyPropertyPathElementNode(avaloniaPropertyFieldMaybe,
-                                XamlIlAvaloniaPropertyHelper.GetAvaloniaPropertyType(avaloniaPropertyFieldMaybe, context.GetAvaloniaTypes(), lineInfo)));
-                        }
-                        else
-                        {
-                            var clrProperty = GetAllDefinedProperties(targetType).FirstOrDefault(p => p.Name == propName.PropertyName);
+                            IXamlType targetType = targetTypeResolver();
+                            var avaloniaPropertyFieldNameMaybe = propName.PropertyName + "Property";
+                            var avaloniaPropertyFieldMaybe = targetType.GetAllFields().FirstOrDefault(f =>
+                                f.IsStatic && f.IsPublic && f.Name == avaloniaPropertyFieldNameMaybe);
 
-                            if (clrProperty is null)
+                            if (avaloniaPropertyFieldMaybe != null)
+                            {
+                                nodes.Add(new XamlIlAvaloniaPropertyPropertyPathElementNode(avaloniaPropertyFieldMaybe,
+                                    XamlIlAvaloniaPropertyHelper.GetAvaloniaPropertyType(avaloniaPropertyFieldMaybe, context.GetAvaloniaTypes(), lineInfo)));
+                            }
+                            else
                             {
-                                throw new XamlX.XamlParseException($"Unable to resolve property of name '{propName.PropertyName}' on type '{targetType}'.", lineInfo);
+                                var clrProperty = GetAllDefinedProperties(targetType).FirstOrDefault(p => p.Name == propName.PropertyName);
+
+                                if (clrProperty is null)
+                                {
+                                    throw new XamlX.XamlParseException($"Unable to resolve property of name '{propName.PropertyName}' on type '{targetType}'.", lineInfo);
+                                }
+                                nodes.Add(new XamlIlClrPropertyPathElementNode(clrProperty));
                             }
-                            nodes.Add(new XamlIlClrPropertyPathElementNode(clrProperty));
+                            break;
                         }
-                        break;
                     case BindingExpressionGrammar.IndexerNode indexer:
                         {
+                            IXamlType targetType = targetTypeResolver();
                             if (targetType.IsArray)
                             {
                                 nodes.Add(new XamlIlArrayIndexerPathElementNode(targetType, indexer.Arguments, lineInfo));
@@ -183,7 +192,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                             XamlIlAvaloniaPropertyHelper.GetAvaloniaPropertyType(avaloniaPropertyField, context.GetAvaloniaTypes(), lineInfo)));
                         break;
                     case BindingExpressionGrammar.SelfNode _:
-                        nodes.Add(new SelfPathElementNode(targetType));
+                        nodes.Add(new SelfPathElementNode(selfType));
                         break;
                     case VisualAncestorBindingExpressionNode visualAncestor:
                         nodes.Add(new FindVisualAncestorPathElementNode(visualAncestor.Type, visualAncestor.Level));
diff --git a/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj b/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
index ac6aced8cb..86132c5d27 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
+++ b/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <DefineConstants>$(DefineConstants);PCL;NETSTANDARD;NETSTANDARD2_0;HAS_TYPE_CONVERTER;HAS_CUSTOM_ATTRIBUTE_PROVIDER;XAMLX_INTERNAL</DefineConstants>
     <UseCecil>false</UseCecil>
     <DefineConstants Condition="$(UseCecil) == true">$(DefineConstants);RUNTIME_XAML_CECIL</DefineConstants>
diff --git a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs
index 41de2355aa..0125156750 100644
--- a/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs
+++ b/src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs
@@ -71,5 +71,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         public CompiledBindingPath Path { get; set; }
 
         public object Source { get; set; }
+
+        public Type DataType { get; set; }
     }
 }
diff --git a/src/Markup/Avalonia.Markup/Avalonia.Markup.csproj b/src/Markup/Avalonia.Markup/Avalonia.Markup.csproj
index c8f60924c6..21370b3bf5 100644
--- a/src/Markup/Avalonia.Markup/Avalonia.Markup.csproj
+++ b/src/Markup/Avalonia.Markup/Avalonia.Markup.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <RootNamespace>Avalonia</RootNamespace>
   </PropertyGroup>
   <ItemGroup>
diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
index 953a7e9a15..a9fc18474c 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs
@@ -25,6 +25,7 @@ namespace Avalonia.Markup.Parsers
             Traversal,
             TypeName,
             Property,
+            AttachedProperty,
             Template,
             End,
         }
@@ -74,6 +75,9 @@ namespace Avalonia.Markup.Parsers
                     case State.Name:
                         (state, syntax) = ParseName(ref r);
                         break;
+                    case State.AttachedProperty:
+                        (state, syntax) = ParseAttachedProperty(ref r);
+                        break;
                 }
                 if (syntax != null)
                 {
@@ -270,11 +274,15 @@ namespace Avalonia.Markup.Parsers
             return (State.CanHaveType, ParseType(ref r, new OfTypeSyntax()));
         }
 
-        private static (State, ISyntax) ParseProperty(ref CharacterReader r)
+        private static (State, ISyntax?) ParseProperty(ref CharacterReader r)
         {
             var property = r.ParseIdentifier();
 
-            if (!r.TakeIf('='))
+            if (r.TakeIf('('))
+            {
+                return (State.AttachedProperty, default);
+            }
+            else if (!r.TakeIf('='))
             {
                 throw new ExpressionParseException(r.Position, $"Expected '=', got '{r.Peek}'");
             }
@@ -286,6 +294,42 @@ namespace Avalonia.Markup.Parsers
             return (State.CanHaveType, new PropertySyntax { Property = property.ToString(), Value = value.ToString() });
         }
 
+        private static (State, ISyntax) ParseAttachedProperty(ref CharacterReader r)
+        {
+            var syntax = ParseType(ref r, new AttachedPropertySyntax());
+            if (!r.TakeIf('.'))
+            {
+                throw new ExpressionParseException(r.Position, $"Expected '.', got '{r.Peek}'");
+            }
+            var property = r.ParseIdentifier();
+            if (property.IsEmpty)
+            {
+                throw new ExpressionParseException(r.Position, $"Expected Attached Property Name, got '{r.Peek}'");
+            }
+            syntax.Property = property.ToString();
+
+            if (!r.TakeIf(')'))
+            {
+                throw new ExpressionParseException(r.Position, $"Expected ')', got '{r.Peek}'");
+            }
+
+            if (!r.TakeIf('='))
+            {
+                throw new ExpressionParseException(r.Position, $"Expected '=', got '{r.Peek}'");
+            }
+
+            var value = r.TakeUntil(']');
+
+            syntax.Value = value.ToString();
+
+            r.Take();
+
+            var state = r.End
+                ? State.End
+                : State.Middle;
+            return (state, syntax);
+        }
+
         private static TSyntax ParseType<TSyntax>(ref CharacterReader r, TSyntax syntax)
             where TSyntax : ITypeSyntax
         {
@@ -461,6 +505,26 @@ namespace Avalonia.Markup.Parsers
             }
         }
 
+        public class AttachedPropertySyntax : ISyntax, ITypeSyntax
+        {
+            public string Xmlns { get; set; } = string.Empty;
+
+            public string TypeName { get; set; } = string.Empty;
+
+            public string Property { get; set; } = string.Empty;
+
+            public string Value { get; set; } = string.Empty;
+
+            public override bool Equals(object? obj)
+            {
+                return obj is AttachedPropertySyntax syntax
+                    && syntax.Xmlns == Xmlns
+                    && syntax.TypeName == TypeName
+                    && syntax.Property == Property
+                    && syntax.Value == Value;
+            }
+        }
+
         public class IsSyntax : ISyntax, ITypeSyntax
         {
             public string TypeName { get; set; } = string.Empty;
diff --git a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorParser.cs b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorParser.cs
index 0a3986ce2b..5b6522064a 100644
--- a/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorParser.cs
+++ b/src/Markup/Avalonia.Markup/Markup/Parsers/SelectorParser.cs
@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using Avalonia.Styling;
 using Avalonia.Utilities;
+using System.Linq;
 
 namespace Avalonia.Markup.Parsers
 {
@@ -75,34 +76,78 @@ namespace Avalonia.Markup.Parsers
                                 throw new InvalidOperationException($"Cannot find '{property.Property}' on '{type}");
                             }
 
+                            {
+                                object? typedValue;
+
+                                if (TypeUtilities.TryConvert(
+                                        targetProperty.PropertyType,
+                                        property.Value,
+                                        CultureInfo.InvariantCulture,
+                                        out typedValue))
+                                {
+                                    result = result.PropertyEquals(targetProperty, typedValue);
+                                }
+                                else
+                                {
+                                    throw new InvalidOperationException(
+                                        $"Could not convert '{property.Value}' to '{targetProperty.PropertyType}");
+                                }
+                            }
+                            break;
+                        }
+                    case SelectorGrammar.AttachedPropertySyntax attachedProperty:
+                        var targetType = result?.TargetType;
+
+                        if (targetType == null)
+                        {
+                            throw new InvalidOperationException("Attached Property selectors must be applied to a type.");
+                        }
+
+                        var attachedPropertyOwnerType = Resolve(attachedProperty.Xmlns, attachedProperty.TypeName);
+
+                        if (attachedPropertyOwnerType is null)
+                        {
+                            throw new InvalidOperationException($"Cannot find '{attachedProperty.Xmlns}:{attachedProperty.TypeName}");
+                        }
+
+                        var targetAttachedProperty = AvaloniaPropertyRegistry.Instance.GetRegisteredAttached(targetType)
+                            .FirstOrDefault(ap => ap.OwnerType == attachedPropertyOwnerType && ap.Name == attachedProperty.Property);
+
+                        if (targetAttachedProperty == null)
+                        {
+                            throw new InvalidOperationException($"Cannot find '{attachedProperty.Property}' on '{attachedPropertyOwnerType}");
+                        }
+
+                        {
                             object? typedValue;
 
                             if (TypeUtilities.TryConvert(
-                                    targetProperty.PropertyType,
-                                    property.Value,
+                                    targetAttachedProperty.PropertyType,
+                                    attachedProperty.Value,
                                     CultureInfo.InvariantCulture,
                                     out typedValue))
                             {
-                                result = result.PropertyEquals(targetProperty, typedValue);
+                                result = result.PropertyEquals(targetAttachedProperty, typedValue);
                             }
                             else
                             {
                                 throw new InvalidOperationException(
-                                    $"Could not convert '{property.Value}' to '{targetProperty.PropertyType}");
+                                    $"Could not convert '{attachedProperty.Value}' to '{targetAttachedProperty.PropertyType}");
                             }
-                            break;
                         }
+
+                        break;
                     case SelectorGrammar.ChildSyntax child:
-                        result = result.Child();
+                        result = result!.Child();
                         break;
                     case SelectorGrammar.DescendantSyntax descendant:
                         result = result.Descendant();
                         break;
                     case SelectorGrammar.TemplateSyntax template:
-                        result = result.Template();
+                        result = result!.Template();
                         break;
                     case SelectorGrammar.NotSyntax not:
-                        result = result.Not(x => Create(not.Argument));
+                        result = result.Not(x => Create(not.Argument)!);
                         break;
                     case SelectorGrammar.NthChildSyntax nth:
                         result = result.NthChild(nth.Step, nth.Offset);
diff --git a/src/Skia/Avalonia.Skia/Avalonia.Skia.csproj b/src/Skia/Avalonia.Skia/Avalonia.Skia.csproj
index 11a64c10ae..bc14494f6a 100644
--- a/src/Skia/Avalonia.Skia/Avalonia.Skia.csproj
+++ b/src/Skia/Avalonia.Skia/Avalonia.Skia.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <RootNamespace>Avalonia.Skia</RootNamespace>
     <AssemblyName>Avalonia.Skia</AssemblyName>
     <PackageId>Avalonia.Skia</PackageId>
diff --git a/src/Skia/Avalonia.Skia/Gpu/ISkiaGpu.cs b/src/Skia/Avalonia.Skia/Gpu/ISkiaGpu.cs
index 32818dfdd2..4a7d4d4ac8 100644
--- a/src/Skia/Avalonia.Skia/Gpu/ISkiaGpu.cs
+++ b/src/Skia/Avalonia.Skia/Gpu/ISkiaGpu.cs
@@ -20,8 +20,8 @@ namespace Avalonia.Skia
         /// <summary>
         /// Creates an offscreen render target surface
         /// </summary>
-        /// <param name="size">size in pixels</param>
-        /// <param name="session">current Skia render session</param>
+        /// <param name="size">size in pixels.</param>
+        /// <param name="session">An optional custom render session.</param>
         ISkiaSurface TryCreateSurface(PixelSize size, ISkiaGpuRenderSession session);
     }
     
diff --git a/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs b/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs
index 8cd4d7b111..3e9849d4dc 100644
--- a/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs
+++ b/src/Web/Avalonia.Web.Blazor/RazorViewTopLevelImpl.cs
@@ -106,8 +106,7 @@ namespace Avalonia.Web.Blazor
 
         public IRenderer CreateRenderer(IRenderRoot root)
         {
-            var loop = AvaloniaLocator.Current.GetService<IRenderLoop>();
-
+            var loop = AvaloniaLocator.Current.GetRequiredService<IRenderLoop>();
             return new DeferredRenderer(root, loop);
         }
 
diff --git a/src/Web/Avalonia.Web.Blazor/WindowingPlatform.cs b/src/Web/Avalonia.Web.Blazor/WindowingPlatform.cs
index 4804016ab2..f30a36b8c9 100644
--- a/src/Web/Avalonia.Web.Blazor/WindowingPlatform.cs
+++ b/src/Web/Avalonia.Web.Blazor/WindowingPlatform.cs
@@ -98,8 +98,7 @@ namespace Avalonia.Web.Blazor
 
         private static IRuntimePlatform GetRuntimePlatform()
         {
-            return AvaloniaLocator.Current.GetService<IRuntimePlatform>() ??
-                throw new InvalidOperationException("Unable to locate IRuntimePlatform.");
+            return AvaloniaLocator.Current.GetRequiredService<IRuntimePlatform>();
         }
     }
 }
diff --git a/src/Windows/Avalonia.Direct2D1/Avalonia.Direct2D1.csproj b/src/Windows/Avalonia.Direct2D1/Avalonia.Direct2D1.csproj
index d6c3368b7d..bc529208ea 100644
--- a/src/Windows/Avalonia.Direct2D1/Avalonia.Direct2D1.csproj
+++ b/src/Windows/Avalonia.Direct2D1/Avalonia.Direct2D1.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <PackageId>Avalonia.Direct2D1</PackageId>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
diff --git a/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj b/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
index c8f08a5799..f433e455a7 100644
--- a/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
+++ b/src/Windows/Avalonia.Win32/Avalonia.Win32.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <PackageId>Avalonia.Win32</PackageId>
   </PropertyGroup>
diff --git a/src/Windows/Avalonia.Win32/FramebufferManager.cs b/src/Windows/Avalonia.Win32/FramebufferManager.cs
index 119edcebbf..7f4b1c976d 100644
--- a/src/Windows/Avalonia.Win32/FramebufferManager.cs
+++ b/src/Windows/Avalonia.Win32/FramebufferManager.cs
@@ -107,8 +107,7 @@ namespace Avalonia.Win32
 
         private static FramebufferData AllocateFramebufferData(int width, int height)
         {
-            var service = AvaloniaLocator.Current.GetService<IRuntimePlatform>() ??
-                throw new InvalidOperationException("Unable to locate IRuntimePlatform.");
+            var service = AvaloniaLocator.Current.GetRequiredService<IRuntimePlatform>();
             var bitmapBlob = service.AllocBlob(width * height * _bytesPerPixel);
 
             return new FramebufferData(bitmapBlob, width, height);
diff --git a/tests/Avalonia.Controls.UnitTests/ButtonTests.cs b/tests/Avalonia.Controls.UnitTests/ButtonTests.cs
index e7a42c2d93..f4acf5ea37 100644
--- a/tests/Avalonia.Controls.UnitTests/ButtonTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ButtonTests.cs
@@ -295,6 +295,20 @@ namespace Avalonia.Controls.UnitTests
             target.CommandParameter = false;
             Assert.False(target.IsEffectivelyEnabled);
         }
+        
+        [Fact]
+        public void Button_Invokes_Doesnt_Execute_When_Button_Disabled()
+        {
+            var target = new Button();
+            var raised = 0;
+
+            target.IsEnabled = false;
+            target.Click += (s, e) => ++raised;
+
+            target.RaiseEvent(new RoutedEventArgs(AccessKeyHandler.AccessKeyPressedEvent));
+
+            Assert.Equal(0, raised);
+        }
 
         private class TestButton : Button, IRenderRoot
         {
diff --git a/tests/Avalonia.Controls.UnitTests/CalendarDatePickerTests.cs b/tests/Avalonia.Controls.UnitTests/CalendarDatePickerTests.cs
index d77c7b87fa..a73e14939d 100644
--- a/tests/Avalonia.Controls.UnitTests/CalendarDatePickerTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/CalendarDatePickerTests.cs
@@ -105,7 +105,11 @@ namespace Avalonia.Controls.UnitTests
                 var calendar =
                     new Calendar
                     {
-                        Name = "PART_Calendar"
+                        Name = "PART_Calendar", 
+                        [!Calendar.SelectedDateProperty] = control[!CalendarDatePicker.SelectedDateProperty],
+                        [!Calendar.DisplayDateProperty] = control[!CalendarDatePicker.DisplayDateProperty],
+                        [!Calendar.DisplayDateStartProperty] = control[!CalendarDatePicker.DisplayDateStartProperty],
+                        [!Calendar.DisplayDateEndProperty] = control[!CalendarDatePicker.DisplayDateEndProperty]
                     }.RegisterInNameScope(scope);
                 var popup =
                     new Popup
diff --git a/tests/Avalonia.Input.UnitTests/TouchDeviceTests.cs b/tests/Avalonia.Input.UnitTests/TouchDeviceTests.cs
new file mode 100644
index 0000000000..7f6d711ccf
--- /dev/null
+++ b/tests/Avalonia.Input.UnitTests/TouchDeviceTests.cs
@@ -0,0 +1,248 @@
+using System;
+using Avalonia.Input.Raw;
+using Avalonia.Platform;
+using Avalonia.UnitTests;
+using Moq;
+using Xunit;
+
+namespace Avalonia.Input.UnitTests
+{
+    public class TouchDeviceTests
+    {
+        [Fact]
+        public void Tapped_Event_Is_Fired_With_Touch()
+        {
+            using var app = UnitTestApp(new TimeSpan(200));
+            var root = new TestRoot();
+            var touchDevice = new TouchDevice();
+
+            var isTapped = false;
+            var executedTimes = 0;
+            root.Tapped += (a, e) =>
+            {
+                isTapped = true;
+                executedTimes++;
+            };
+            TapOnce(InputManager.Instance, touchDevice, root);
+            Assert.True(isTapped);
+            Assert.Equal(1, executedTimes);
+
+        }
+
+        [Fact]
+        public void DoubleTapped_Event_Is_Fired_With_Touch()
+        {
+            using var app = UnitTestApp(new TimeSpan(200));
+            var root = new TestRoot();
+            var touchDevice = new TouchDevice();
+
+            var isDoubleTapped = false;
+            var doubleTappedExecutedTimes = 0;
+            var tappedExecutedTimes = 0;
+            root.DoubleTapped += (a, e) =>
+            {
+                isDoubleTapped = true;
+                doubleTappedExecutedTimes++;
+            };
+            root.Tapped += (a, e) =>
+            {
+                tappedExecutedTimes++;
+            };
+            TapOnce(InputManager.Instance, touchDevice, root);
+            TapOnce(InputManager.Instance, touchDevice, root, touchPointId: 1);
+            Assert.Equal(1, tappedExecutedTimes);
+            Assert.True(isDoubleTapped);
+            Assert.Equal(1, doubleTappedExecutedTimes);
+        }
+
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        [InlineData(4)]
+        [InlineData(5)]
+        public void PointerPressed_Counts_Clicks_Correctly(int clickCount)
+        {
+            using var app = UnitTestApp(new TimeSpan(200));
+            var root = new TestRoot();
+            var touchDevice = new TouchDevice();
+
+            var pointerPressedExecutedTimes = 0;
+            var pointerPressedClicks = 0;
+            root.PointerPressed += (a, e) =>
+            {
+                pointerPressedClicks = e.ClickCount;
+                pointerPressedExecutedTimes++;
+            };
+            for (int i = 0; i < clickCount; i++)
+            {
+                TapOnce(InputManager.Instance, touchDevice, root, touchPointId: i);
+            }
+
+            Assert.Equal(clickCount, pointerPressedExecutedTimes);
+            Assert.Equal(pointerPressedClicks, clickCount);
+        }
+
+        [Fact]
+        public void DoubleTapped_Not_Fired_When_Click_Too_Late()
+        {
+            using var app = UnitTestApp(new TimeSpan(0, 0, 0, 0, 20));
+            var root = new TestRoot();
+            var touchDevice = new TouchDevice();
+
+            var isDoubleTapped = false;
+            var doubleTappedExecutedTimes = 0;
+            var tappedExecutedTimes = 0;
+            root.DoubleTapped += (a, e) =>
+            {
+                isDoubleTapped = true;
+                doubleTappedExecutedTimes++;
+            };
+            root.Tapped += (a, e) =>
+            {
+                tappedExecutedTimes++;
+            };
+            TapOnce(InputManager.Instance, touchDevice, root);
+            TapOnce(InputManager.Instance, touchDevice, root, 21, 1);
+            Assert.Equal(2, tappedExecutedTimes);
+            Assert.False(isDoubleTapped);
+            Assert.Equal(0, doubleTappedExecutedTimes);
+
+        }
+
+        [Fact]
+        public void DoubleTapped_Not_Fired_When_Second_Click_Is_From_Different_Touch_Contact()
+        {
+            using var app = UnitTestApp(new TimeSpan(200));
+            var root = new TestRoot();
+            var touchDevice = new TouchDevice();
+
+            var isDoubleTapped = false;
+            var doubleTappedExecutedTimes = 0;
+            var tappedExecutedTimes = 0;
+            root.DoubleTapped += (a, e) =>
+            {
+                isDoubleTapped = true;
+                doubleTappedExecutedTimes++;
+            };
+            root.Tapped += (a, e) =>
+            {
+                tappedExecutedTimes++;
+            };
+            SendXTouchContactsWithIds(InputManager.Instance, touchDevice, root, RawPointerEventType.TouchBegin, 0, 1);
+            SendXTouchContactsWithIds(InputManager.Instance, touchDevice, root, RawPointerEventType.TouchEnd, 0, 1);
+            Assert.Equal(2, tappedExecutedTimes);
+            Assert.False(isDoubleTapped);
+            Assert.Equal(0, doubleTappedExecutedTimes);
+        }
+
+        [Fact]
+        public void Click_Counting_Should_Work_Correctly_With_Few_Touch_Contacts()
+        {
+            using var app = UnitTestApp(new TimeSpan(200));
+
+            var root = new TestRoot();
+            var touchDevice = new TouchDevice();
+
+            var pointerPressedExecutedTimes = 0;
+            var tappedExecutedTimes = 0;
+            var isDoubleTapped = false;
+            var doubleTappedExecutedTimes = 0;
+            root.PointerPressed += (a, e) =>
+            {
+                pointerPressedExecutedTimes++;
+                switch (pointerPressedExecutedTimes)
+                {
+                    case <= 2:
+                        Assert.True(e.ClickCount == 1);
+                        break;
+                    case 3:
+                        Assert.True(e.ClickCount == 2);
+                        break;
+                    case 4:
+                        Assert.True(e.ClickCount == 3);
+                        break;
+                    case 5:
+                        Assert.True(e.ClickCount == 4);
+                        break;
+                    case 6:
+                        Assert.True(e.ClickCount == 5);
+                        break;
+                    case 7:
+                        Assert.True(e.ClickCount == 1);
+                        break;
+                    case 8:
+                        Assert.True(e.ClickCount == 1);
+                        break;
+                    case 9:
+                        Assert.True(e.ClickCount == 2);
+                        break;
+                    default:
+                        break;
+                }
+            };
+            root.DoubleTapped += (a, e) =>
+            {
+                isDoubleTapped = true;
+                doubleTappedExecutedTimes++;
+            };
+            root.Tapped += (a, e) =>
+            {
+                tappedExecutedTimes++;
+            };
+            SendXTouchContactsWithIds(InputManager.Instance, touchDevice, root, RawPointerEventType.TouchBegin, 0, 1);
+            SendXTouchContactsWithIds(InputManager.Instance, touchDevice, root, RawPointerEventType.TouchEnd, 0, 1);
+            TapOnce(InputManager.Instance, touchDevice, root, touchPointId: 2);
+            TapOnce(InputManager.Instance, touchDevice, root, touchPointId: 3);
+            TapOnce(InputManager.Instance, touchDevice, root, touchPointId: 4);
+            SendXTouchContactsWithIds(InputManager.Instance, touchDevice, root, RawPointerEventType.TouchBegin, 5, 6, 7);
+            SendXTouchContactsWithIds(InputManager.Instance, touchDevice, root, RawPointerEventType.TouchEnd, 5, 6, 7);
+            TapOnce(InputManager.Instance, touchDevice, root, touchPointId: 8);
+            Assert.Equal(6, tappedExecutedTimes);
+            Assert.Equal(9, pointerPressedExecutedTimes);
+            Assert.True(isDoubleTapped);
+            Assert.Equal(3, doubleTappedExecutedTimes);
+        }
+
+        private IDisposable UnitTestApp(TimeSpan doubleClickTime = new TimeSpan())
+        {
+            var unitTestApp = UnitTestApplication.Start(
+                new TestServices(inputManager: new InputManager()));
+            var iSettingsMock = new Mock<IPlatformSettings>();
+            iSettingsMock.Setup(x => x.DoubleClickTime).Returns(doubleClickTime);
+            AvaloniaLocator.CurrentMutable.BindToSelf(this)
+               .Bind<IPlatformSettings>().ToConstant(iSettingsMock.Object);
+            return unitTestApp;
+        }
+        
+        private static void SendXTouchContactsWithIds(IInputManager inputManager, TouchDevice device, IInputRoot root, RawPointerEventType type, params long[] touchPointIds)
+        {
+            for (int i = 0; i < touchPointIds.Length; i++)
+            {
+                inputManager.ProcessInput(new RawTouchEventArgs(device, 0,
+                                                              root,
+                                                              type,
+                                                              new Point(0, 0),
+                                                              RawInputModifiers.None,
+                                                              touchPointIds[i]));
+            }
+        }
+
+
+        private static void TapOnce(IInputManager inputManager, TouchDevice device, IInputRoot root, ulong timestamp = 0, long touchPointId = 0)
+        {
+            inputManager.ProcessInput(new RawTouchEventArgs(device, timestamp,
+                                               root,
+                                               RawPointerEventType.TouchBegin,
+                                               new Point(0, 0),
+                                               RawInputModifiers.None,
+                                               touchPointId));
+            inputManager.ProcessInput(new RawTouchEventArgs(device, timestamp,
+                                                root,
+                                                RawPointerEventType.TouchEnd,
+                                                new Point(0, 0),
+                                                RawInputModifiers.None,
+                                                touchPointId));
+        }
+    }
+}
diff --git a/tests/Avalonia.Markup.UnitTests/Parsers/SelectorGrammarTests.cs b/tests/Avalonia.Markup.UnitTests/Parsers/SelectorGrammarTests.cs
index 568f6deaf2..6fbf024ff1 100644
--- a/tests/Avalonia.Markup.UnitTests/Parsers/SelectorGrammarTests.cs
+++ b/tests/Avalonia.Markup.UnitTests/Parsers/SelectorGrammarTests.cs
@@ -197,6 +197,42 @@ namespace Avalonia.Markup.UnitTests.Parsers
                 result);
         }
 
+        [Fact]
+        public void OfType_AttachedProperty()
+        {
+            var result = SelectorGrammar.Parse("Button[(Grid.Column)=1]");
+
+            Assert.Equal(
+                new SelectorGrammar.ISyntax[]
+                {
+                    new SelectorGrammar.OfTypeSyntax { TypeName = "Button" },
+                    new SelectorGrammar.AttachedPropertySyntax { 
+                        Xmlns = string.Empty,
+                        TypeName="Grid",
+                        Property = "Column",
+                        Value = "1" },
+                },
+                result);
+        }
+
+        [Fact]
+        public void OfType_AttachedProperty_WithNamespace()
+        {
+            var result = SelectorGrammar.Parse("Button[(x|Grid.Column)=1]");
+
+            Assert.Equal(
+                new SelectorGrammar.ISyntax[]
+                {
+                    new SelectorGrammar.OfTypeSyntax { TypeName = "Button" },
+                    new SelectorGrammar.AttachedPropertySyntax {
+                        Xmlns = "x",
+                        TypeName="Grid",
+                        Property = "Column",
+                        Value = "1" },
+                },
+                result);
+        }
+
         [Fact]
         public void Not_OfType()
         {
diff --git a/tests/Avalonia.Markup.UnitTests/Parsers/SelectorParserTests.cs b/tests/Avalonia.Markup.UnitTests/Parsers/SelectorParserTests.cs
index 1c0cba56c9..338bdb3ae1 100644
--- a/tests/Avalonia.Markup.UnitTests/Parsers/SelectorParserTests.cs
+++ b/tests/Avalonia.Markup.UnitTests/Parsers/SelectorParserTests.cs
@@ -7,6 +7,25 @@ namespace Avalonia.Markup.UnitTests.Parsers
 {
     public class SelectorParserTests
     {
+        static SelectorParserTests()
+        {
+            //Ensure the attached properties are registered before run tests
+            System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(typeof(Grid).TypeHandle);
+            System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(typeof(Auth).TypeHandle);
+        }
+
+        class Auth
+        {
+            public readonly static AttachedProperty<string> NameProperty =
+                AvaloniaProperty.RegisterAttached<Auth, AvaloniaObject, string>("Name");
+
+            public static string GetName(AvaloniaObject avaloniaObject) =>
+                avaloniaObject.GetValue(NameProperty);
+
+            public static void SetName(AvaloniaObject avaloniaObject, string value) =>
+                avaloniaObject.SetValue(NameProperty, value);
+        }
+
         [Fact]
         public void Parses_Boolean_Property_Selector()
         {
@@ -14,6 +33,36 @@ namespace Avalonia.Markup.UnitTests.Parsers
             var result = target.Parse("TextBlock[IsPointerOver=True]");
         }
 
+        [Fact]
+        public void Parses_AttacchedProperty_Selector_With_Namespace()
+        {
+            var target = new SelectorParser((ns, type) =>
+                {
+                    return (ns, type) switch
+                    {
+                        ("", nameof(TextBlock)) => typeof(TextBlock),
+                        ("l",nameof(Auth)) => typeof(Auth),
+                        _ => null
+                    };
+                });
+            var result = target.Parse("TextBlock[(l|Auth.Name)=Admin]");
+        }
+
+        [Fact]
+        public void Parses_AttacchedProperty_Selector()
+        {
+            var target = new SelectorParser((ns, type) =>
+            {
+                return (ns, type) switch
+                {
+                    ("", nameof(TextBlock)) => typeof(TextBlock),
+                    ("", nameof(Grid)) => typeof(Grid),
+                    _ => null
+                };
+            });
+            var result = target.Parse("TextBlock[(Grid.Column)=1]");
+        }
+
         [Fact]
         public void Parses_Comma_Separated_Selectors()
         {
diff --git a/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/CompiledBindingExtensionTests.cs b/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/CompiledBindingExtensionTests.cs
index 8a61458030..15c6f5877f 100644
--- a/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/CompiledBindingExtensionTests.cs
+++ b/tests/Avalonia.Markup.Xaml.UnitTests/MarkupExtensions/CompiledBindingExtensionTests.cs
@@ -731,8 +731,7 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
 <Window xmlns='https://github.com/avaloniaui'
         xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
         xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'
-        Title='foo'
-        x:DataType='local:TestDataContext'>
+        Title='foo'>
     <ContentControl Content='{CompiledBinding $parent.Title}' Name='contentControl' />
 </Window>";
                 var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
@@ -1042,6 +1041,27 @@ namespace Avalonia.Markup.Xaml.UnitTests.MarkupExtensions
             }
         }
 
+        [Fact]
+        public void Binds_To_Self_Without_DataType()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.MarkupExtensions;assembly=Avalonia.Markup.Xaml.UnitTests'>
+    <TextBlock Name='textBlock' Text='{CompiledBinding $self.Name}' />
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                var textBlock = window.FindControl<TextBlock>("textBlock");
+
+                window.ApplyTemplate();
+                window.Presenter.ApplyTemplate();
+
+                Assert.Equal(textBlock.Name, textBlock.Text);
+            }
+        }
+
         void Throws(string type, Action cb)
         {
             try
diff --git a/tests/Avalonia.Styling.UnitTests/SelectorTests_PropertyEquals.cs b/tests/Avalonia.Styling.UnitTests/SelectorTests_PropertyEquals.cs
index 7689a458ae..729b42196b 100644
--- a/tests/Avalonia.Styling.UnitTests/SelectorTests_PropertyEquals.cs
+++ b/tests/Avalonia.Styling.UnitTests/SelectorTests_PropertyEquals.cs
@@ -8,6 +8,73 @@ namespace Avalonia.Styling.UnitTests
 {
     public class SelectorTests_PropertyEquals
     {
+        static SelectorTests_PropertyEquals()
+        {
+            //Ensure the attached properties are registered before run tests
+            System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(typeof(Grid).TypeHandle);
+            System.Runtime.CompilerServices.RuntimeHelpers.RunClassConstructor(typeof(Auth).TypeHandle);
+        }
+
+        class Auth
+        {
+            public readonly static AttachedProperty<string> NameProperty =
+                AvaloniaProperty.RegisterAttached<Auth, AvaloniaObject, string>("Name");
+
+            public static string GetName(AvaloniaObject avaloniaObject) =>
+                avaloniaObject.GetValue(NameProperty);
+
+            public static void SetName(AvaloniaObject avaloniaObject, string value) =>
+                avaloniaObject.SetValue(NameProperty, value);
+        }
+
+        [Fact]
+        public async Task PropertyEquals_Attached_Property_Matching_Value()
+        {
+            var target = new Markup.Parsers.SelectorParser((ns, type) =>
+            {
+                return (ns, type) switch
+                {
+                    ("", nameof(TextBlock)) => typeof(TextBlock),
+                    ("", nameof(Grid)) => typeof(Grid),
+                    _ => null
+                };
+            }).Parse("TextBlock[(Grid.Column)=1]");
+            
+
+            var control = new TextBlock();
+            var activator = target.Match(control).Activator.ToObservable();
+
+            Assert.False(await activator.Take(1));
+            Grid.SetColumn(control, 1);
+            Assert.True(await activator.Take(1));
+            Grid.SetColumn(control, 0);
+            Assert.False(await activator.Take(1));
+        }
+
+        [Fact]
+        public async Task PropertyEquals_Attached_Property_With_Namespace_Matching_Value()
+        {
+            var target = new Markup.Parsers.SelectorParser((ns, type) =>
+            {
+                return (ns, type) switch
+                {
+                    ("", nameof(TextBlock)) => typeof(TextBlock),
+                    ("l", nameof(Auth)) => typeof(Auth),
+                    _ => null
+                };
+            }).Parse("TextBlock[(l|Auth.Name)=Admin]");
+
+
+            var control = new TextBlock();
+            var activator = target.Match(control).Activator.ToObservable();
+
+            Assert.False(await activator.Take(1));
+            Auth.SetName(control, "Admin");
+            Assert.True(await activator.Take(1));
+            Auth.SetName(control, null);
+            Assert.False(await activator.Take(1));
+        }
+
         [Fact]
         public async Task PropertyEquals_Matches_When_Property_Has_Matching_Value()
         {
diff --git a/tests/Avalonia.Visuals.UnitTests/Rendering/SceneGraph/TextNodeTests.cs b/tests/Avalonia.Visuals.UnitTests/Rendering/SceneGraph/TextNodeTests.cs
index 7c5ec5ddfd..a6eaea334c 100644
--- a/tests/Avalonia.Visuals.UnitTests/Rendering/SceneGraph/TextNodeTests.cs
+++ b/tests/Avalonia.Visuals.UnitTests/Rendering/SceneGraph/TextNodeTests.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
+using Avalonia.Media;
 using Avalonia.Platform;
 using Avalonia.Rendering.SceneGraph;
 using Moq;
@@ -15,7 +16,7 @@ namespace Avalonia.Visuals.UnitTests.Rendering.SceneGraph
         {
             var target = new TextNode(
                 Matrix.Identity,
-                null,
+                Brushes.Black,
                 new Point(10, 10),
                 Mock.Of<IFormattedTextImpl>(x => x.Bounds == new Rect(5, 5, 50, 50)));