Nullable annotations for Markup.Xaml

src/Avalonia.Base/Styling/ITemplate.cs

@@ -2,6 +2,6 @@
 {
     public interface ITemplate
     {
-        object Build();
+        object? Build();
     }
 }

src/Avalonia.Controls/Primitives/TemplatedControl.cs

@@ -286,14 +286,17 @@ namespace Avalonia.Controls.Primitives
                 {
                     Logger.TryGet(LogEventLevel.Verbose, LogArea.Control)?.Log(this, "Creating control template");
 
-                    var (child, nameScope) = template.Build(this);
-                    ApplyTemplatedParent(child, this);
-                    ((ISetLogicalParent)child).SetParent(this);
-                    VisualChildren.Add(child);
-
-                    var e = new TemplateAppliedEventArgs(nameScope);
-                    OnApplyTemplate(e);
-                    RaiseEvent(e);
+                    if (template.Build(this) is { } templateResult)
+                    {
+                        var (child, nameScope) = templateResult;
+                        ApplyTemplatedParent(child, this);
+                        ((ISetLogicalParent)child).SetParent(this);
+                        VisualChildren.Add(child);
+
+                        var e = new TemplateAppliedEventArgs(nameScope);
+                        OnApplyTemplate(e);
+                        RaiseEvent(e);
+                    }
                 }
 
                 _appliedTemplate = template;

src/Avalonia.Controls/Templates/IControlTemplate.cs

@@ -1,13 +1,11 @@
-using System;
 using Avalonia.Controls.Primitives;
-using Avalonia.Styling;
 
 namespace Avalonia.Controls.Templates
 {
     /// <summary>
     /// Interface representing a template used to build a <see cref="TemplatedControl"/>.
     /// </summary>
-    public interface IControlTemplate : ITemplate<TemplatedControl, ControlTemplateResult>
+    public interface IControlTemplate : ITemplate<TemplatedControl, ControlTemplateResult?>
     {
     }
 

src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj

@@ -58,7 +58,6 @@
         <Compile Include="XamlIl\Runtime\IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs" />
         <Compile Include="XamlIl\Runtime\XamlIlRuntimeHelpers.cs" />
         <Compile Include="XamlLoadException.cs" />
-        <Compile Include="..\Avalonia.Markup\Markup\Parsers\BindingExpressionGrammar.cs" />
         <Compile Include="XamlTypes.cs" />
     </ItemGroup>
   <ItemGroup>
@@ -69,6 +68,7 @@
   <Import Project="..\..\..\build\ApiDiff.props" />
   <Import Project="..\..\..\build\DevAnalyzers.props" />
   <Import Project="..\..\..\build\TrimmingEnable.props" />
+  <Import Project="..\..\..\build\NullableEnable.props" />
 
   <ItemGroup Label="InternalsVisibleTo">
     <InternalsVisibleTo Include="Avalonia.Markup.Xaml.UnitTests, PublicKey=$(AvaloniaPublicKey)" />

src/Markup/Avalonia.Markup.Xaml/AvaloniaXamlLoader.cs

@@ -1,8 +1,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
-using System.IO;
 using Avalonia.Platform;
-#nullable enable
+
 namespace Avalonia.Markup.Xaml
 {
     /// <summary>
@@ -79,7 +78,7 @@ namespace Avalonia.Markup.Xaml
 
             var compiledLoader = assetLocator.GetAssembly(uri, baseUri)
                 ?.GetType("CompiledAvaloniaXaml.!XamlLoader")
-                ?.GetMethod("TryLoad", new[] { typeof(System.IServiceProvider), typeof(string) });
+                ?.GetMethod("TryLoad", new[] { typeof(IServiceProvider), typeof(string) });
             if (compiledLoader != null)
             {
                 var compiledResult = compiledLoader.Invoke(null, new object?[] { sp, absoluteUri.ToString()});

src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaPropertyTypeConverter.cs

@@ -14,18 +14,20 @@ namespace Avalonia.Markup.Xaml.Converters
     [RequiresUnreferencedCode(TrimmingMessages.XamlTypeResolvedRequiresUnreferenceCodeMessage)]
     public class AvaloniaPropertyTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var registry = AvaloniaPropertyRegistry.Instance;
             var (ns, owner, propertyName) = PropertyParser.Parse(new CharacterReader(((string)value).AsSpan()));
             var ownerType = TryResolveOwnerByName(context, ns, owner);
-            var targetType = context.GetFirstParent<ControlTemplate>()?.TargetType ??
-                context.GetFirstParent<Style>()?.Selector?.TargetType ??
+            var targetType = context?.GetFirstParent<ControlTemplate>()?.TargetType ??
+                context?.GetFirstParent<Style>()?.Selector?.TargetType ??
                 typeof(Control);
             var effectiveOwner = ownerType ?? targetType;
             var property = registry.FindRegistered(effectiveOwner, propertyName);
@@ -51,11 +53,11 @@ namespace Avalonia.Markup.Xaml.Converters
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.XamlTypeResolvedRequiresUnreferenceCodeMessage)]
-        private static Type TryResolveOwnerByName(ITypeDescriptorContext context, string ns, string owner)
+        private static Type? TryResolveOwnerByName(ITypeDescriptorContext? context, string? ns, string? owner)
         {
             if (owner != null)
             {
-                var result = context.ResolveType(ns, owner);
+                var result = context?.ResolveType(ns, owner);
 
                 if (result == null)
                 {

src/Markup/Avalonia.Markup.Xaml/Converters/AvaloniaUriTypeConverter.cs

@@ -6,12 +6,14 @@ namespace Avalonia.Markup.Xaml.Converters
 {
     public class AvaloniaUriTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var s = value as string;
             if (s == null)

src/Markup/Avalonia.Markup.Xaml/Converters/BitmapTypeConverter.cs

@@ -1,20 +1,21 @@
 using System;
+using System.ComponentModel;
 using System.Globalization;
 using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-    using System.ComponentModel;
-
     public class BitmapTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var s = (string)value;
             var uri = s.StartsWith("/")
@@ -25,7 +26,7 @@ namespace Avalonia.Markup.Xaml.Converters
                 return new Bitmap(uri.LocalPath);
 
             var assets = AvaloniaLocator.Current.GetRequiredService<IAssetLoader>();
-            return new Bitmap(assets.Open(uri, context.GetContextBaseUri()));
+            return new Bitmap(assets.Open(uri, context?.GetContextBaseUri()));
         }
     }
 }

src/Markup/Avalonia.Markup.Xaml/Converters/ColorToBrushConverter.cs

@@ -23,7 +23,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is a <see cref="Color"/> and <paramref name="targetType"/>
         /// is <see cref="IBrush"/> then converts the color to a solid color brush.
         /// </returns>
-        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
         {
             return Convert(value, targetType);
         }
@@ -40,7 +40,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is an <see cref="ISolidColorBrush"/> and <paramref name="targetType"/>
         /// is <see cref="Color"/> then converts the solid color brush to a color.
         /// </returns>
-        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
         {
             return ConvertBack(value, targetType);
         }
@@ -55,7 +55,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is a <see cref="Color"/> and <paramref name="targetType"/>
         /// is <see cref="IBrush"/> then converts the color to a solid color brush.
         /// </returns>
-        public static object Convert(object value, Type targetType)
+        public static object? Convert(object? value, Type? targetType)
         {
             if (targetType == typeof(IBrush) && value is Color c)
             {
@@ -75,7 +75,7 @@ namespace Avalonia.Markup.Xaml.Converters
         /// If <paramref name="value"/> is an <see cref="ISolidColorBrush"/> and <paramref name="targetType"/>
         /// is <see cref="Color"/> then converts the solid color brush to a color.
         /// </returns>
-        public static object ConvertBack(object value, Type targetType)
+        public static object? ConvertBack(object? value, Type? targetType)
         {
             if (targetType == typeof(Color) && value is ISolidColorBrush brush)
             {

src/Markup/Avalonia.Markup.Xaml/Converters/FontFamilyTypeConverter.cs

@@ -1,24 +1,24 @@
 using System;
 using System.ComponentModel;
 using System.Globalization;
-
 using Avalonia.Media;
 
-
 namespace Avalonia.Markup.Xaml.Converters
 {
     public class FontFamilyTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var s = (string)value;
 
-            return FontFamily.Parse(s, context.GetContextBaseUri());
+            return FontFamily.Parse(s, context?.GetContextBaseUri());
         }
     }
 }

src/Markup/Avalonia.Markup.Xaml/Converters/IconTypeConverter.cs

@@ -2,20 +2,21 @@
 using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 using System;
+using System.ComponentModel;
 using System.Globalization;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-	using System.ComponentModel;
-
     public class IconTypeConverter : TypeConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
         {
             return sourceType == typeof(string);
         }
 
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var path = value as string;
             if (path != null)
@@ -32,7 +33,7 @@ namespace Avalonia.Markup.Xaml.Converters
             throw new NotSupportedException();
         }
 
-        private static WindowIcon CreateIconFromPath(ITypeDescriptorContext context, string s)
+        private static WindowIcon CreateIconFromPath(ITypeDescriptorContext? context, string s)
         {
             var uri = s.StartsWith("/")
                 ? new Uri(s, UriKind.Relative)
@@ -41,7 +42,7 @@ namespace Avalonia.Markup.Xaml.Converters
             if(uri.IsAbsoluteUri && uri.IsFile)
                 return new WindowIcon(uri.LocalPath);
             var assets = AvaloniaLocator.Current.GetRequiredService<IAssetLoader>();
-            return new WindowIcon(assets.Open(uri, context.GetContextBaseUri()));
+            return new WindowIcon(assets.Open(uri, context?.GetContextBaseUri()));
         }
     }
 }

src/Markup/Avalonia.Markup.Xaml/Converters/PointsListTypeConverter.cs

@@ -1,20 +1,19 @@
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Globalization;
+using Avalonia.Utilities;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-    using System.ComponentModel;
-    using Avalonia.Utilities;
-
     public class PointsListTypeConverter : 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)
         {
             var points = new List<Point>();
 

src/Markup/Avalonia.Markup.Xaml/Converters/TimeSpanTypeConverter.cs

@@ -1,18 +1,13 @@
 using System;
+using System.ComponentModel;
 using System.Globalization;
 
 namespace Avalonia.Markup.Xaml.Converters
 {
-	using System.ComponentModel;
-
-    public class TimeSpanTypeConverter : System.ComponentModel.TimeSpanConverter
+    public class TimeSpanTypeConverter : TimeSpanConverter
     {
-        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
-        {
-            return base.CanConvertFrom(context, sourceType);
-        }
-
-        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        /// <inheritdoc />
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             var valueStr = (string)value;
             if (!valueStr.Contains(':'))

src/Markup/Avalonia.Markup.Xaml/Extensions.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using Avalonia.Controls;
@@ -11,38 +10,38 @@ namespace Avalonia.Markup.Xaml
 {
     internal static class Extensions
     {
-        public static T GetService<T>(this IServiceProvider sp) => (T)sp?.GetService(typeof(T));
-        
-        
-        public static Uri GetContextBaseUri(this IServiceProvider ctx) => ctx.GetService<IUriContext>().BaseUri;
+        public static T? GetService<T>(this IServiceProvider sp) => (T?)sp.GetService(typeof(T));
+
+        public static T GetRequiredService<T>(this IServiceProvider sp)
+            => sp.GetService<T>() ?? throw new InvalidOperationException($"Service {typeof(T)} hasn't been registered");
 
-        public static T GetFirstParent<T>(this IServiceProvider ctx) where T : class 
-            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>().Parents.OfType<T>().FirstOrDefault();
+        public static Uri? GetContextBaseUri(this IServiceProvider ctx) => ctx.GetService<IUriContext>()?.BaseUri;
 
-        public static T GetLastParent<T>(this IServiceProvider ctx) where T : class 
-            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>().Parents.OfType<T>().LastOrDefault();
+        public static T? GetFirstParent<T>(this IServiceProvider ctx) where T : class
+            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>()?.Parents.OfType<T>().FirstOrDefault();
+
+        public static T? GetLastParent<T>(this IServiceProvider ctx) where T : class
+            => ctx.GetService<IAvaloniaXamlIlParentStackProvider>()?.Parents.OfType<T>().LastOrDefault();
 
         public static IEnumerable<T> GetParents<T>(this IServiceProvider sp)
-        {
-            return sp.GetService<IAvaloniaXamlIlParentStackProvider>().Parents.OfType<T>();
-        }
+            => sp.GetService<IAvaloniaXamlIlParentStackProvider>()?.Parents.OfType<T>() ?? Enumerable.Empty<T>();
 
         public static bool IsInControlTemplate(this IServiceProvider sp) => sp.GetService<IAvaloniaXamlIlControlTemplateProvider>() != null;
 
         [RequiresUnreferencedCode(TrimmingMessages.XamlTypeResolvedRequiresUnreferenceCodeMessage)]
-        public static Type ResolveType(this IServiceProvider ctx, string namespacePrefix, string type)
+        public static Type ResolveType(this IServiceProvider ctx, string? namespacePrefix, string type)
         {
             var tr = ctx.GetService<IXamlTypeResolver>();
             string name = string.IsNullOrEmpty(namespacePrefix) ? type : $"{namespacePrefix}:{type}";
-            return tr?.Resolve(name);
+            return tr?.Resolve(name) ?? throw new XamlLoadException($"Could not find type '{name}'.");
         }
         
-        public static object GetDefaultAnchor(this IServiceProvider provider)
+        public static object? GetDefaultAnchor(this IServiceProvider provider)
         {
             // If the target is not a control, so we need to find an anchor that will let us look
             // up named controls and style resources. First look for the closest Control in
             // the context.
-            object anchor = provider.GetFirstParent<Control>();
+            object? anchor = provider.GetFirstParent<Control>();
 
             if (anchor is null)
             {

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs

@@ -35,7 +35,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             };
         }
 
-        private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty targetProperty, object anchor, bool enableDataValidation)
+        private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty? targetProperty, object? anchor, bool enableDataValidation)
         {
             if (Source != null)
             {
@@ -61,8 +61,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             }
             else
             {
+                var styledElement = target as StyledElement
+                    ?? anchor as StyledElement
+                    ?? throw new ArgumentException($"Cannot find a valid {nameof(StyledElement)} to use as the binding source.");
+
                 return CreateSourceObserver(
-                    (target as StyledElement) ?? (anchor as StyledElement),
+                    styledElement,
                     Path.BuildExpression(enableDataValidation));
             }
         }
@@ -70,8 +74,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         [ConstructorArgument("path")]
         public CompiledBindingPath Path { get; set; }
 
-        public object Source { get; set; }
+        public object? Source { get; set; }
 
-        public Type DataType { get; set; }
+        public Type? DataType { get; set; }
     }
 }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ArrayElementPlugin.cs

@@ -1,13 +1,11 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
-using System.Text;
 using Avalonia.Data;
 using Avalonia.Data.Core.Plugins;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class ArrayElementPlugin : IPropertyAccessorPlugin
+    internal class ArrayElementPlugin : IPropertyAccessorPlugin
     {
         private readonly int[] _indices;
         private readonly Type _elementType;
@@ -25,7 +23,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
-        public IPropertyAccessor Start(WeakReference<object> reference, string propertyName)
+        public IPropertyAccessor? Start(WeakReference<object?> reference, string propertyName)
         {
             if (reference.TryGetTarget(out var target) && target is Array arr)
             {
@@ -48,9 +46,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             public override Type PropertyType { get; }
 
-            public override object Value => _reference.TryGetTarget(out var arr) ? arr.GetValue(_indices) : null;
+            public override object? Value => _reference.TryGetTarget(out var arr) ? arr.GetValue(_indices) : null;
 
-            public override bool SetValue(object value, BindingPriority priority)
+            public override bool SetValue(object? value, BindingPriority priority)
             {
                 if (_reference.TryGetTarget(out var arr))
                 {

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CommandAccessorPlugin.cs

@@ -2,8 +2,6 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
-using System.Reflection;
-using System.Text;
 using System.Windows.Input;
 using Avalonia.Data;
 using Avalonia.Data.Core.Plugins;
@@ -13,11 +11,11 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     internal class CommandAccessorPlugin : IPropertyAccessorPlugin
     {
-        private readonly Action<object, object> _execute;
-        private readonly Func<object, object, bool> _canExecute;
+        private readonly Action<object, object?> _execute;
+        private readonly Func<object, object?, bool>? _canExecute;
         private readonly ISet<string> _dependsOnProperties;
 
-        public CommandAccessorPlugin(Action<object, object> execute, Func<object, object, bool> canExecute, ISet<string> dependsOnProperties)
+        public CommandAccessorPlugin(Action<object, object?> execute, Func<object, object?, bool>? canExecute, ISet<string> dependsOnProperties)
         {
             _execute = execute;
             _canExecute = canExecute;
@@ -31,18 +29,18 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
-        public IPropertyAccessor Start(WeakReference<object> reference, string propertyName)
+        public IPropertyAccessor Start(WeakReference<object?> reference, string propertyName)
         {
             return new CommandAccessor(reference, _execute, _canExecute, _dependsOnProperties);
         }
 
         private sealed class CommandAccessor : PropertyAccessorBase
         {
-            private readonly WeakReference<object> _reference;
-            private Command _command;
+            private readonly WeakReference<object?> _reference;
+            private readonly Command _command;
             private readonly ISet<string> _dependsOnProperties;
 
-            public CommandAccessor(WeakReference<object> reference, Action<object, object> execute, Func<object, object, bool> canExecute, ISet<string> dependsOnProperties)
+            public CommandAccessor(WeakReference<object?> reference, Action<object, object?> execute, Func<object, object?, bool>? canExecute, ISet<string> dependsOnProperties)
             {
                 _reference = reference ?? throw new ArgumentNullException(nameof(reference));
                 _dependsOnProperties = dependsOnProperties;
@@ -50,7 +48,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             }
 
-            public override object Value => _reference.TryGetTarget(out var _) ? _command : null;
+            public override object? Value => _reference.TryGetTarget(out _) ? _command : null;
 
             private void RaiseCanExecuteChanged()
             {
@@ -59,13 +57,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             private sealed class Command : ICommand
             {
-                private readonly WeakReference<object> _target;
-                private readonly Action<object, object> _execute;
-                private readonly Func<object, object, bool> _canExecute;
+                private readonly WeakReference<object?> _target;
+                private readonly Action<object, object?> _execute;
+                private readonly Func<object, object?, bool>? _canExecute;
 
-                public event EventHandler CanExecuteChanged;
+                public event EventHandler? CanExecuteChanged;
 
-                public Command(WeakReference<object> target, Action<object, object> execute, Func<object, object, bool> canExecute)
+                public Command(WeakReference<object?> target, Action<object, object?> execute, Func<object, object?, bool>? canExecute)
                 {
                     _target = target;
                     _execute = execute;
@@ -78,7 +76,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                        , Threading.DispatcherPriority.Input);
                 }
 
-                public bool CanExecute(object parameter)
+                public bool CanExecute(object? parameter)
                 {
                     if (_target.TryGetTarget(out var target))
                     {
@@ -91,7 +89,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                     return false;
                 }
 
-                public void Execute(object parameter)
+                public void Execute(object? parameter)
                 {
                     if (_target.TryGetTarget(out var target))
                     {
@@ -102,12 +100,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
             public override Type PropertyType => typeof(ICommand);
 
-            public override bool SetValue(object value, BindingPriority priority)
+            public override bool SetValue(object? value, BindingPriority priority)
             {
                 return false;
             }
 
-            void OnNotifyPropertyChanged(object sender, PropertyChangedEventArgs e)
+            private void OnNotifyPropertyChanged(object? sender, PropertyChangedEventArgs e)
             {
                 if (string.IsNullOrEmpty(e.PropertyName) || _dependsOnProperties.Contains(e.PropertyName))
                 {

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/CompiledBindingPath.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         public CompiledBindingPath()
             => _elements = Array.Empty<ICompiledBindingPathElement>();
 
-        internal CompiledBindingPath(ICompiledBindingPathElement[] elements, object rawSource)
+        internal CompiledBindingPath(ICompiledBindingPathElement[] elements, object? rawSource)
         {
             _elements = elements;
             RawSource = rawSource;
@@ -26,14 +26,14 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = TrimmingMessages.CompiledBindingSafeSupressWarningMessage)]
         internal ExpressionNode BuildExpression(bool enableValidation)
         {
-            ExpressionNode pathRoot = null;
-            ExpressionNode path = null;
+            ExpressionNode? pathRoot = null;
+            ExpressionNode? path = null;
             foreach (var element in _elements)
             {
-                ExpressionNode node = null;
+                ExpressionNode? node;
                 switch (element)
                 {
-                    case NotExpressionPathElement _:
+                    case NotExpressionPathElement:
                         node = new LogicalNotNode();
                         break;
                     case PropertyElement prop:
@@ -54,7 +54,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                     case AncestorPathElement ancestor:
                         node = new FindAncestorNode(ancestor.AncestorType, ancestor.Level);
                         break;
-                    case SelfPathElement _:
+                    case SelfPathElement:
                         node = new SelfNode();
                         break;
                     case ElementNameElement name:
@@ -70,7 +70,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                         throw new InvalidOperationException($"Unknown binding path element type {element.GetType().FullName}");
                 }
 
-                path = pathRoot is null ? (pathRoot = node) : path.Next = node;
+                path = pathRoot is null ? (pathRoot = node) : path!.Next = node;
             }
 
             return pathRoot ?? new EmptyExpressionNode();
@@ -81,16 +81,17 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         internal SourceMode SourceMode => Array.Exists(_elements, e => e is IControlSourceBindingPathElement)
             ? SourceMode.Control : SourceMode.Data;
 
-        internal object RawSource { get; }
+        internal object? RawSource { get; }
 
+        /// <inheritdoc />
         public override string ToString()
             => string.Concat((IEnumerable<ICompiledBindingPathElement>) _elements);
     }
 
     public class CompiledBindingPathBuilder
     {
-        private object _rawSource;
-        private List<ICompiledBindingPathElement> _elements = new List<ICompiledBindingPathElement>();
+        private object? _rawSource;
+        private readonly List<ICompiledBindingPathElement> _elements = new();
 
         public CompiledBindingPathBuilder Not()
         {
@@ -98,7 +99,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return this;
         }
 
-        public CompiledBindingPathBuilder Property(IPropertyInfo info, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory)
+        public CompiledBindingPathBuilder Property(IPropertyInfo info, Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> accessorFactory)
         {
             _elements.Add(new PropertyElement(info, accessorFactory, _elements.Count == 0));
             return this;
@@ -110,7 +111,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return this;
         }
 
-        public CompiledBindingPathBuilder Command(string methodName, Action<object, object> executeHelper, Func<object, object, bool> canExecuteHelper, string[] dependsOnProperties)
+        public CompiledBindingPathBuilder Command(string methodName, Action<object, object?> executeHelper, Func<object, object?, bool>? canExecuteHelper, string[]? dependsOnProperties)
         {
             _elements.Add(new MethodAsCommandElement(methodName, executeHelper, canExecuteHelper, dependsOnProperties ?? Array.Empty<string>()));
             return this;
@@ -163,7 +164,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return this;
         }
 
-        public CompiledBindingPathBuilder SetRawSource(object rawSource)
+        public CompiledBindingPathBuilder SetRawSource(object? rawSource)
         {
             _rawSource = rawSource;
             return this;
@@ -187,7 +188,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
     {
         private readonly bool _isFirstElement;
 
-        public PropertyElement(IPropertyInfo property, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory, bool isFirstElement)
+        public PropertyElement(IPropertyInfo property, Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> accessorFactory, bool isFirstElement)
         {
             Property = property;
             AccessorFactory = accessorFactory;
@@ -196,7 +197,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
         public IPropertyInfo Property { get; }
 
-        public Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> AccessorFactory { get; }
+        public Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> AccessorFactory { get; }
 
         public override string ToString()
             => _isFirstElement ? Property.Name : $".{Property.Name}";
@@ -206,7 +207,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
     {
         public MethodAsDelegateElement(RuntimeMethodHandle method, RuntimeTypeHandle delegateType)
         {
-            Method = (MethodInfo)MethodBase.GetMethodFromHandle(method);
+            Method = MethodBase.GetMethodFromHandle(method) as MethodInfo
+                ?? throw new ArgumentException("Invalid method handle", nameof(method));
             DelegateType = Type.GetTypeFromHandle(delegateType);
         }
 
@@ -217,7 +219,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class MethodAsCommandElement : ICompiledBindingPathElement
     {
-        public MethodAsCommandElement(string methodName, Action<object, object> executeHelper, Func<object, object, bool> canExecuteHelper, string[] dependsOnElements)
+        public MethodAsCommandElement(string methodName, Action<object, object?> executeHelper, Func<object, object?, bool>? canExecuteHelper, string[] dependsOnElements)
         {
             MethodName = methodName;
             ExecuteMethod = executeHelper;
@@ -226,8 +228,8 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         public string MethodName { get; }
-        public Action<object, object> ExecuteMethod { get; }
-        public Func<object, object, bool> CanExecuteMethod { get; }
+        public Action<object, object?> ExecuteMethod { get; }
+        public Func<object, object?, bool>? CanExecuteMethod { get; }
         public HashSet<string> DependsOnProperties { get; }
     }
 
@@ -240,7 +242,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
     {
         Type Type { get; }
 
-        Func<object, object> Cast { get; }
+        Func<object?, object?> Cast { get; }
     }
 
     internal class TaskStreamPathElement<T> : IStronglyTypedStreamElement
@@ -267,13 +269,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class AncestorPathElement : ICompiledBindingPathElement, IControlSourceBindingPathElement
     {
-        public AncestorPathElement(Type ancestorType, int level)
+        public AncestorPathElement(Type? ancestorType, int level)
         {
             AncestorType = ancestorType;
             Level = level;
         }
 
-        public Type AncestorType { get; }
+        public Type? AncestorType { get; }
         public int Level { get; }
 
         public override string ToString()
@@ -282,13 +284,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class VisualAncestorPathElement : ICompiledBindingPathElement, IControlSourceBindingPathElement
     {
-        public VisualAncestorPathElement(Type ancestorType, int level)
+        public VisualAncestorPathElement(Type? ancestorType, int level)
         {
             AncestorType = ancestorType;
             Level = level;
         }
 
-        public Type AncestorType { get; }
+        public Type? AncestorType { get; }
         public int Level { get; }
     }
 
@@ -323,7 +325,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class TypeCastPathElement<T> : ITypeCastElement
     {
-        private static object TryCast(object obj)
+        private static object? TryCast(object? obj)
         {
             if (obj is T result)
                 return result;
@@ -332,7 +334,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
         public Type Type => typeof(T);
 
-        public Func<object, object> Cast => TryCast;
+        public Func<object?, object?> Cast => TryCast;
 
         public override string ToString()
             => $"({Type.FullName})";

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/FindVisualAncestorNode.cs

@@ -5,13 +5,13 @@ using Avalonia.Reactive;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class FindVisualAncestorNode : ExpressionNode
+    internal class FindVisualAncestorNode : ExpressionNode
     {
         private readonly int _level;
-        private readonly Type _ancestorType;
-        private IDisposable _subscription;
+        private readonly Type? _ancestorType;
+        private IDisposable? _subscription;
 
-        public FindVisualAncestorNode(Type ancestorType, int level)
+        public FindVisualAncestorNode(Type? ancestorType, int level)
         {
             _level = level;
             _ancestorType = ancestorType;
@@ -32,9 +32,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             }
         }
 
-        protected override void StartListeningCore(WeakReference<object> reference)
+        protected override void StartListeningCore(WeakReference<object?> reference)
         {
-            if (reference.TryGetTarget(out object target) && target is Visual visual)
+            if (reference.TryGetTarget(out object? target) && target is Visual visual)
             {
                 _subscription = VisualLocator.Track(visual, _level, _ancestorType).Subscribe(ValueChanged);
             }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/MethodAccessorPlugin.cs

@@ -1,19 +1,15 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
-using System.Text;
 using Avalonia.Data;
 using Avalonia.Data.Core.Plugins;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     internal class MethodAccessorPlugin : IPropertyAccessorPlugin
     {
-        private MethodInfo _method;
+        private readonly MethodInfo _method;
         private readonly Type _delegateType;
 
         public MethodAccessorPlugin(MethodInfo method, Type delegateType)

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/ObservableStreamPlugin.cs

@@ -1,33 +1,31 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
-using System.Text;
 using Avalonia.Data.Core.Plugins;
 using Avalonia.Reactive;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class ObservableStreamPlugin<T> : IStreamPlugin
+    internal class ObservableStreamPlugin<T> : IStreamPlugin
     {
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public bool Match(WeakReference<object> reference)
+        public bool Match(WeakReference<object?> reference)
         {
             return reference.TryGetTarget(out var target) && target is IObservable<T>;
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public IObservable<object> Start(WeakReference<object> reference)
+        public IObservable<object?> Start(WeakReference<object?> reference)
         {
             if (!(reference.TryGetTarget(out var target) && target is IObservable<T> obs))
             {
-                return Observable.Empty<object>();
+                return Observable.Empty<object?>();
             }
-            else if (target is IObservable<object> obj)
+            else if (target is IObservable<object?> obj)
             {
                 return obj;
             }
 
-            return obs.Select(x => (object)x);
+            return obs.Select(x => (object?)x);
         }
     }
 }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorFactory.cs

@@ -11,29 +11,29 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     public static class PropertyInfoAccessorFactory
     {
-        public static IPropertyAccessor CreateInpcPropertyAccessor(WeakReference<object> target, IPropertyInfo property)
+        public static IPropertyAccessor CreateInpcPropertyAccessor(WeakReference<object?> target, IPropertyInfo property)
             => new InpcPropertyAccessor(target, property);
 
-        public static IPropertyAccessor CreateAvaloniaPropertyAccessor(WeakReference<object> target, IPropertyInfo property)
-            => new AvaloniaPropertyAccessor(new WeakReference<AvaloniaObject>((AvaloniaObject)(target.TryGetTarget(out var o) ? o : null)), (AvaloniaProperty)property);
+        public static IPropertyAccessor CreateAvaloniaPropertyAccessor(WeakReference<object?> target, IPropertyInfo property)
+            => new AvaloniaPropertyAccessor(new WeakReference<AvaloniaObject?>((AvaloniaObject?)(target.TryGetTarget(out var o) ? o : null)), (AvaloniaProperty)property);
 
-        public static IPropertyAccessor CreateIndexerPropertyAccessor(WeakReference<object> target, IPropertyInfo property, int argument)
+        public static IPropertyAccessor CreateIndexerPropertyAccessor(WeakReference<object?> target, IPropertyInfo property, int argument)
             => new IndexerAccessor(target, property, argument);
     }
 
     internal class AvaloniaPropertyAccessor : PropertyAccessorBase
     {
-        private readonly WeakReference<AvaloniaObject> _reference;
+        private readonly WeakReference<AvaloniaObject?> _reference;
         private readonly AvaloniaProperty _property;
-        private IDisposable _subscription;
+        private IDisposable? _subscription;
 
-        public AvaloniaPropertyAccessor(WeakReference<AvaloniaObject> reference, AvaloniaProperty property)
+        public AvaloniaPropertyAccessor(WeakReference<AvaloniaObject?> reference, AvaloniaProperty property)
         {
-            _reference = reference ?? throw new ArgumentNullException(nameof(reference));;
-            _property = property ?? throw new ArgumentNullException(nameof(property));;
+            _reference = reference ?? throw new ArgumentNullException(nameof(reference));
+            _property = property ?? throw new ArgumentNullException(nameof(property));
         }
 
-        public AvaloniaObject Instance
+        public AvaloniaObject? Instance
         {
             get
             {
@@ -43,13 +43,13 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         public override Type PropertyType => _property.PropertyType;
-        public override object Value => Instance?.GetValue(_property);
+        public override object? Value => Instance?.GetValue(_property);
 
-        public override bool SetValue(object value, BindingPriority priority)
+        public override bool SetValue(object? value, BindingPriority priority)
         {
-            if (!_property.IsReadOnly)
+            if (!_property.IsReadOnly && Instance is { } instance)
             {
-                Instance.SetValue(_property, value, priority);
+                instance.SetValue(_property, value, priority);
                 return true;
             }
 
@@ -70,10 +70,10 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class InpcPropertyAccessor : PropertyAccessorBase, IWeakEventSubscriber<PropertyChangedEventArgs>
     {
-        protected readonly WeakReference<object> _reference;
+        protected readonly WeakReference<object?> _reference;
         private readonly IPropertyInfo _property;
 
-        public InpcPropertyAccessor(WeakReference<object> reference, IPropertyInfo property)
+        public InpcPropertyAccessor(WeakReference<object?> reference, IPropertyInfo property)
         {
             _reference = reference ?? throw new ArgumentNullException(nameof(reference));
             _property = property ?? throw new ArgumentNullException(nameof(property));
@@ -81,7 +81,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
         public override Type PropertyType => _property.PropertyType;
 
-        public override object Value
+        public override object? Value
         {
             get
             {
@@ -89,7 +89,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             }
         }
 
-        public override bool SetValue(object value, BindingPriority priority)
+        public override bool SetValue(object? value, BindingPriority priority)
         {
             if (_property.CanSet && _reference.TryGetTarget(out var o))
             {
@@ -103,7 +103,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             return false;
         }
 
-        public void OnEvent(object sender, WeakEvent ev, PropertyChangedEventArgs e)
+        public void OnEvent(object? sender, WeakEvent ev, PropertyChangedEventArgs e)
         {
             if (e.PropertyName == _property.Name || string.IsNullOrEmpty(e.PropertyName))
             {
@@ -144,9 +144,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 
     internal class IndexerAccessor : InpcPropertyAccessor, IWeakEventSubscriber<NotifyCollectionChangedEventArgs>
     {
-        private int _index;
+        private readonly int _index;
 
-        public IndexerAccessor(WeakReference<object> target, IPropertyInfo basePropertyInfo, int argument)
+        public IndexerAccessor(WeakReference<object?> target, IPropertyInfo basePropertyInfo, int argument)
             :base(target, basePropertyInfo)
         {
             _index = argument;
@@ -167,7 +167,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                 WeakEvents.CollectionChanged.Unsubscribe(incc, this);
         }
         
-        public void OnEvent(object sender, WeakEvent ev, NotifyCollectionChangedEventArgs args)
+        public void OnEvent(object? sender, WeakEvent ev, NotifyCollectionChangedEventArgs args)
         {
             if (ShouldNotifyListeners(args))
             {
@@ -175,7 +175,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
             }
         }
 
-        bool ShouldNotifyListeners(NotifyCollectionChangedEventArgs e)
+        private bool ShouldNotifyListeners(NotifyCollectionChangedEventArgs e)
         {
             switch (e.Action)
             {
@@ -185,12 +185,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                     return _index >= e.OldStartingIndex;
                 case NotifyCollectionChangedAction.Replace:
                     return _index >= e.NewStartingIndex &&
-                           _index < e.NewStartingIndex + e.NewItems.Count;
+                           _index < e.NewStartingIndex + e.NewItems!.Count;
                 case NotifyCollectionChangedAction.Move:
                     return (_index >= e.NewStartingIndex &&
-                            _index < e.NewStartingIndex + e.NewItems.Count) ||
+                            _index < e.NewStartingIndex + e.NewItems!.Count) ||
                            (_index >= e.OldStartingIndex &&
-                            _index < e.OldStartingIndex + e.OldItems.Count);
+                            _index < e.OldStartingIndex + e.OldItems!.Count);
                 case NotifyCollectionChangedAction.Reset:
                     return true;
             }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/PropertyInfoAccessorPlugin.cs

@@ -1,20 +1,17 @@
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
-using System.Text;
-using Avalonia.Data;
 using Avalonia.Data.Core;
 using Avalonia.Data.Core.Plugins;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class PropertyInfoAccessorPlugin : IPropertyAccessorPlugin
+    internal class PropertyInfoAccessorPlugin : IPropertyAccessorPlugin
     {
         private readonly IPropertyInfo _propertyInfo;
-        private readonly Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> _accessorFactory;
+        private readonly Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> _accessorFactory;
 
-        public PropertyInfoAccessorPlugin(IPropertyInfo propertyInfo, Func<WeakReference<object>, IPropertyInfo, IPropertyAccessor> accessorFactory)
+        public PropertyInfoAccessorPlugin(IPropertyInfo propertyInfo, Func<WeakReference<object?>, IPropertyInfo, IPropertyAccessor> accessorFactory)
         {
             _propertyInfo = propertyInfo;
             _accessorFactory = accessorFactory;
@@ -27,7 +24,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
-        public IPropertyAccessor Start(WeakReference<object> reference, string propertyName)
+        public IPropertyAccessor Start(WeakReference<object?> reference, string propertyName)
         {
             Debug.Assert(_propertyInfo.Name == propertyName);
             return _accessorFactory(reference, _propertyInfo);

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/StrongTypeCastNode.cs

@@ -5,14 +5,14 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
     internal class StrongTypeCastNode : TypeCastNode
     {
-        private Func<object, object> _cast;
+        private readonly Func<object?, object?> _cast;
 
-        public StrongTypeCastNode(Type type, Func<object, object> cast) : base(type)
+        public StrongTypeCastNode(Type type, Func<object?, object?> cast) : base(type)
         {
             _cast = cast;
         }
 
-        protected override object Cast(object value)
+        protected override object? Cast(object? value)
             => _cast(value);
     }
 }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindings/TaskStreamPlugin.cs

@@ -7,20 +7,20 @@ using Avalonia.Reactive;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
 {
-    class TaskStreamPlugin<T> : IStreamPlugin
+    internal class TaskStreamPlugin<T> : IStreamPlugin
     {
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public bool Match(WeakReference<object> reference)
+        public bool Match(WeakReference<object?> reference)
         {
             return reference.TryGetTarget(out var target) && target is Task<T>;
         }
 
         [RequiresUnreferencedCode(TrimmingMessages.StreamPluginRequiresUnreferencedCodeMessage)]
-        public IObservable<object> Start(WeakReference<object> reference)
+        public IObservable<object?> Start(WeakReference<object?> reference)
         {
             if(!(reference.TryGetTarget(out var target) && target is Task<T> task))
             {
-                return Observable.Empty<object>();
+                return Observable.Empty<object?>();
             }
 
             switch (task.Status)
@@ -29,9 +29,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
                 case TaskStatus.Faulted:
                     return HandleCompleted(task);
                 default:
-                    var subject = new LightweightSubject<object>();
+                    var subject = new LightweightSubject<object?>();
                     task.ContinueWith(
-                            x => HandleCompleted(task).Subscribe(subject),
+                            _ => HandleCompleted(task).Subscribe(subject),
                             TaskScheduler.FromCurrentSynchronizationContext())
                         .ConfigureAwait(false);
                     return subject;
@@ -39,14 +39,14 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings
         }
         
         
-        private static IObservable<object> HandleCompleted(Task<T> task)
+        private static IObservable<object?> HandleCompleted(Task<T> task)
         {
             switch (task.Status)
             {
                 case TaskStatus.RanToCompletion:
-                    return Observable.Return((object)task.Result);
+                    return Observable.Return((object?)task.Result);
                 case TaskStatus.Faulted:
-                    return Observable.Return(new BindingNotification(task.Exception, BindingErrorType.Error));
+                    return Observable.Return(new BindingNotification(task.Exception!, BindingErrorType.Error));
                 default:
                     throw new AvaloniaInternalException("HandleCompleted called for non-completed Task.");
             }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/DynamicResourceExtension.cs

@@ -4,8 +4,6 @@ using Avalonia.Data;
 using Avalonia.Markup.Xaml.Converters;
 using Avalonia.Media;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions
 {
     public class DynamicResourceExtension : IBinding
@@ -31,7 +29,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
             var provideTarget = serviceProvider.GetService<IProvideValueTarget>();
 
-            if (!(provideTarget.TargetObject is StyledElement))
+            if (provideTarget?.TargetObject is not StyledElement)
             {
                 _anchor = serviceProvider.GetFirstParent<StyledElement>() ??
                     serviceProvider.GetFirstParent<IResourceProvider>() ??

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/On.cs

@@ -1,5 +1,4 @@
-#nullable enable
-using System.Collections.Generic;
+using System.Collections.Generic;
 using Avalonia.Metadata;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions;

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnFormFactorExtension.cs

@@ -1,6 +1,4 @@
-#nullable enable
 using System;
-
 using Avalonia.Metadata;
 using Avalonia.Platform;
 
@@ -20,7 +18,7 @@ public sealed class OnFormFactorExtension : OnFormFactorExtensionBase<object, On
 
     public static bool ShouldProvideOption(IServiceProvider serviceProvider, FormFactorType option)
     {
-        return serviceProvider.GetService<IRuntimePlatform>().GetRuntimeInfo().FormFactor == option;
+        return serviceProvider.GetService<IRuntimePlatform>()?.GetRuntimeInfo().FormFactor == option;
     }
 }
 
@@ -38,7 +36,7 @@ public sealed class OnFormFactorExtension<TReturn> : OnFormFactorExtensionBase<T
 
     public static bool ShouldProvideOption(IServiceProvider serviceProvider, FormFactorType option)
     {
-        return serviceProvider.GetService<IRuntimePlatform>().GetRuntimeInfo().FormFactor == option;
+        return serviceProvider.GetService<IRuntimePlatform>()?.GetRuntimeInfo().FormFactor == option;
     }
 }
 

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/OnPlatformExtension.cs

@@ -1,6 +1,4 @@
-#nullable enable
-using System;
-using Avalonia.Compatibility;
+using Avalonia.Compatibility;
 using Avalonia.Metadata;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions;

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ReflectionBindingExtension.cs

@@ -2,7 +2,6 @@ using Avalonia.Data;
 using System;
 using Avalonia.Controls;
 using Avalonia.Data.Converters;
-using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 
 namespace Avalonia.Markup.Xaml.MarkupExtensions
@@ -21,11 +20,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
         public Binding ProvideValue(IServiceProvider serviceProvider)
         {
-            var descriptorContext = (ITypeDescriptorContext)serviceProvider;
-
             return new Binding
             {
-                TypeResolver = descriptorContext.ResolveType,
+                TypeResolver = serviceProvider.ResolveType,
                 Converter = Converter,
                 ConverterParameter = ConverterParameter,
                 ElementName = ElementName,
@@ -36,33 +33,33 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
                 Source = Source,
                 StringFormat = StringFormat,
                 RelativeSource = RelativeSource,
-                DefaultAnchor = new WeakReference(descriptorContext.GetDefaultAnchor()),
+                DefaultAnchor = new WeakReference(serviceProvider.GetDefaultAnchor()),
                 TargetNullValue = TargetNullValue,
-                NameScope = new WeakReference<INameScope>(serviceProvider.GetService<INameScope>())
+                NameScope = new WeakReference<INameScope?>(serviceProvider.GetService<INameScope>())
             };
         }
 
-        public IValueConverter Converter { get; set; }
+        public IValueConverter? Converter { get; set; }
 
-        public object ConverterParameter { get; set; }
+        public object? ConverterParameter { get; set; }
 
-        public string ElementName { get; set; }
+        public string? ElementName { get; set; }
 
-        public object FallbackValue { get; set; } = AvaloniaProperty.UnsetValue;
+        public object? FallbackValue { get; set; } = AvaloniaProperty.UnsetValue;
 
         public BindingMode Mode { get; set; }
 
         [ConstructorArgument("path")]
-        public string Path { get; set; }
+        public string Path { get; set; } = "";
 
         public BindingPriority Priority { get; set; } = BindingPriority.LocalValue;
 
-        public object Source { get; set; }
+        public object? Source { get; set; }
 
-        public string StringFormat { get; set; }
+        public string? StringFormat { get; set; }
 
-        public RelativeSource RelativeSource { get; set; }
+        public RelativeSource? RelativeSource { get; set; }
 
-        public object TargetNullValue { get; set; } = AvaloniaProperty.UnsetValue;
+        public object? TargetNullValue { get; set; } = AvaloniaProperty.UnsetValue;
     }
 }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/RelativeSourceExtension.cs

@@ -28,7 +28,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         [ConstructorArgument("mode")]
         public RelativeSourceMode Mode { get; set; } = RelativeSourceMode.FindAncestor;
 
-        public Type AncestorType { get; set; }
+        public Type? AncestorType { get; set; }
 
         public TreeType Tree { get; set; }
 

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/ResolveByNameExtension.cs

@@ -2,8 +2,6 @@
 using Avalonia.Controls;
 using Avalonia.Data.Core;
 
-#nullable  enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions
 {
     public class ResolveByNameExtension
@@ -18,6 +16,9 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
         public object? ProvideValue(IServiceProvider serviceProvider)
         {
             var nameScope = serviceProvider.GetService<INameScope>();
+
+            if (nameScope is null)
+                return null;
             
             var value = nameScope.FindAsync(Name);
 
@@ -25,10 +26,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
                 return value.GetResult();
 
             var provideValueTarget = serviceProvider.GetService<IProvideValueTarget>();
-            var target = provideValueTarget.TargetObject;
 
-            if (provideValueTarget.TargetProperty is IPropertyInfo property) 
+            if (provideValueTarget?.TargetProperty is IPropertyInfo property)
+            {
+                var target = provideValueTarget.TargetObject;
                 value.OnCompleted(() => property.Set(target, value.GetResult()));
+            }
 
             return AvaloniaProperty.UnsetValue;
         }

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/StaticResourceExtension.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Reflection;
 using Avalonia.Controls;
 using Avalonia.Markup.Data;
@@ -8,8 +7,6 @@ using Avalonia.Markup.Xaml.Converters;
 using Avalonia.Markup.Xaml.XamlIl.Runtime;
 using Avalonia.Styling;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.MarkupExtensions
 {
     public class StaticResourceExtension
@@ -25,7 +22,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
         public object? ResourceKey { get; set; }
 
-        public object ProvideValue(IServiceProvider serviceProvider)
+        public object? ProvideValue(IServiceProvider serviceProvider)
         {
             if (ResourceKey is not { } resourceKey)
             {
@@ -34,32 +31,37 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
             var stack = serviceProvider.GetService<IAvaloniaXamlIlParentStackProvider>();
             var provideTarget = serviceProvider.GetService<IProvideValueTarget>();
-            var themeVariant = (provideTarget.TargetObject as IThemeVariantHost)?.ActualThemeVariant;
+            var targetObject = provideTarget?.TargetObject;
+            var targetProperty = provideTarget?.TargetProperty;
+            var themeVariant = (targetObject as IThemeVariantHost)?.ActualThemeVariant;
 
-            var targetType = provideTarget.TargetProperty switch
+            var targetType = targetProperty switch
             {
                 AvaloniaProperty ap => ap.PropertyType,
                 PropertyInfo pi => pi.PropertyType,
-                _ => null,
+                _ => null
             };
 
-            if (provideTarget.TargetObject is Setter { Property: not null } setter)
+            if (targetObject is Setter { Property: { } setterProperty })
             {
-                targetType = setter.Property?.PropertyType;
+                targetType = setterProperty.PropertyType;
             }
-            
+
             // Look upwards though the ambient context for IResourceNodes
             // which might be able to give us the resource.
-            foreach (var parent in stack.Parents)
+            if (stack is not null)
             {
-                if (parent is IResourceNode node && node.TryGetResource(resourceKey, themeVariant, out var value))
+                foreach (var parent in stack.Parents)
                 {
-                    return ColorToBrushConverter.Convert(value, targetType);
+                    if (parent is IResourceNode node && node.TryGetResource(resourceKey, themeVariant, out var value))
+                    {
+                        return ColorToBrushConverter.Convert(value, targetType);
+                    }
                 }
             }
 
-            if (provideTarget.TargetObject is Control target &&
-                provideTarget.TargetProperty is PropertyInfo property)
+            if (targetObject is Control target &&
+                targetProperty is PropertyInfo property)
             {
                 // This is stored locally to avoid allocating closure in the outer scope.
                 var localTargetType = targetType;
@@ -72,7 +74,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             throw new KeyNotFoundException($"Static resource '{resourceKey}' not found.");
         }
 
-        private object GetValue(StyledElement control, Type? targetType)
+        private object? GetValue(StyledElement control, Type? targetType)
         {
             return ColorToBrushConverter.Convert(control.FindResource(ResourceKey!), targetType);
         }

src/Markup/Avalonia.Markup.Xaml/Parsers/PropertyParser.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Markup.Xaml.Parsers
 {
     internal class PropertyParser
     {
-        public static (string ns, string owner, string name) Parse(CharacterReader r)
+        public static (string? ns, string? owner, string name) Parse(CharacterReader r)
         {
             if (r.End)
             {
@@ -14,9 +14,9 @@ namespace Avalonia.Markup.Xaml.Parsers
 
             var openParens = r.TakeIf('(');
             bool closeParens = false;
-            string ns = null;
-            string owner = null;
-            string name = null;
+            string? ns = null;
+            string? owner = null;
+            string? name = null;
 
             do
             {

src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderConfiguration.cs

@@ -2,8 +2,6 @@ using System.Reflection;
 
 namespace Avalonia.Markup.Xaml;
 
-#nullable enable
-
 public class RuntimeXamlLoaderConfiguration
 {
     /// <summary>

src/Markup/Avalonia.Markup.Xaml/RuntimeXamlLoaderDocument.cs

@@ -1,5 +1,4 @@
-#nullable enable
-using System;
+using System;
 using System.IO;
 using System.Text;
 

src/Markup/Avalonia.Markup.Xaml/Styling/MergeResourceInclude.cs

@@ -1,8 +1,5 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
-using Avalonia.Controls;
-
-#nullable enable
 
 namespace Avalonia.Markup.Xaml.Styling;
 

src/Markup/Avalonia.Markup.Xaml/Styling/ResourceInclude.cs

@@ -3,8 +3,6 @@ using System.Diagnostics.CodeAnalysis;
 using Avalonia.Controls;
 using Avalonia.Styling;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.Styling
 {
     /// <summary>

src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs

@@ -4,8 +4,6 @@ using Avalonia.Controls;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 
-#nullable enable
-
 namespace Avalonia.Markup.Xaml.Styling
 {
     /// <summary>
@@ -65,11 +63,11 @@ namespace Avalonia.Markup.Xaml.Styling
                     _isLoading = false;
                 }
 
-                return _loaded?[0]!;
+                return _loaded[0];
             }
         }
 
-        bool IResourceNode.HasResources => Loaded?.HasResources ?? false;
+        bool IResourceNode.HasResources => Loaded.HasResources;
 
         IReadOnlyList<IStyle> IStyle.Children => _loaded ?? Array.Empty<IStyle>();
 

src/Markup/Avalonia.Markup.Xaml/Templates/ControlTemplate.cs

@@ -9,10 +9,10 @@ namespace Avalonia.Markup.Xaml.Templates
     {
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public Type TargetType { get; set; }
+        public Type? TargetType { get; set; }
 
-        public ControlTemplateResult Build(TemplatedControl control) => TemplateContent.Load(Content);
+        public ControlTemplateResult? Build(TemplatedControl control) => TemplateContent.Load(Content);
     }
 }

src/Markup/Avalonia.Markup.Xaml/Templates/DataTemplate.cs

@@ -8,13 +8,13 @@ namespace Avalonia.Markup.Xaml.Templates
     public class DataTemplate : IRecyclingDataTemplate, ITypedDataTemplate
     {
         [DataType]
-        public Type DataType { get; set; }
+        public Type? DataType { get; set; }
 
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public bool Match(object data)
+        public bool Match(object? data)
         {
             if (DataType == null)
             {
@@ -26,9 +26,9 @@ namespace Avalonia.Markup.Xaml.Templates
             }
         }
 
-        public Control Build(object data) => Build(data, null);
+        public Control? Build(object? data) => Build(data, null);
 
-        public Control Build(object data, Control existing)
+        public Control? Build(object? data, Control? existing)
         {
             return existing ?? TemplateContent.Load(Content)?.Control;
         }

src/Markup/Avalonia.Markup.Xaml/Templates/ItemsPanelTemplate.cs

@@ -4,14 +4,14 @@ using Avalonia.Styling;
 
 namespace Avalonia.Markup.Xaml.Templates
 {
-    public class ItemsPanelTemplate : ITemplate<Panel>
+    public class ItemsPanelTemplate : ITemplate<Panel?>
     {
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public Panel Build() => (Panel)TemplateContent.Load(Content)?.Control;
+        public Panel? Build() => (Panel?)TemplateContent.Load(Content)?.Control;
 
-        object ITemplate.Build() => Build();
+        object? ITemplate.Build() => Build();
     }
 }

src/Markup/Avalonia.Markup.Xaml/Templates/Template.cs

@@ -4,14 +4,14 @@ using Avalonia.Styling;
 
 namespace Avalonia.Markup.Xaml.Templates
 {
-    public class Template : ITemplate<Control>
+    public class Template : ITemplate<Control?>
     {
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
-        public Control Build() => TemplateContent.Load(Content)?.Control;
+        public Control? Build() => TemplateContent.Load(Content)?.Control;
 
-        object ITemplate.Build() => Build();
+        object? ITemplate.Build() => Build();
     }
 }

src/Markup/Avalonia.Markup.Xaml/Templates/TemplateContent.cs

@@ -3,14 +3,13 @@ using Avalonia.Controls.Templates;
 
 namespace Avalonia.Markup.Xaml.Templates
 {
-    
     public static class TemplateContent
     {
-        public static ControlTemplateResult Load(object templateContent)
+        public static ControlTemplateResult? Load(object? templateContent)
         {
-            if (templateContent is Func<IServiceProvider, object> direct)
+            if (templateContent is Func<IServiceProvider?, object?> direct)
             {
-                return (ControlTemplateResult)direct(null);
+                return (ControlTemplateResult?)direct(null);
             }
 
             if (templateContent is null)
@@ -18,18 +17,18 @@ namespace Avalonia.Markup.Xaml.Templates
                 return null;
             }
 
-            throw new ArgumentException(nameof(templateContent));
+            throw new ArgumentException($"Unexpected content {templateContent.GetType()}", nameof(templateContent));
         }
 
-        public static TemplateResult<T> Load<T>(object templateContent)
+        public static TemplateResult<T>? Load<T>(object? templateContent)
         {
-            if (templateContent is Func<IServiceProvider, object> direct)
-                return (TemplateResult<T>)direct(null);
+            if (templateContent is Func<IServiceProvider?, object?> direct)
+                return (TemplateResult<T>?)direct(null);
 
             if (templateContent is null)
                 return null;
 
-            throw new ArgumentException(nameof(templateContent));
+            throw new ArgumentException($"Unexpected content {templateContent.GetType()}", nameof(templateContent));
         }
     }
 }

src/Markup/Avalonia.Markup.Xaml/Templates/TreeDataTemplate.cs

@@ -13,16 +13,16 @@ namespace Avalonia.Markup.Xaml.Templates
     public class TreeDataTemplate : ITreeDataTemplate, ITypedDataTemplate
     {
         [DataType]
-        public Type DataType { get; set; }
+        public Type? DataType { get; set; }
 
         [Content]
         [TemplateContent]
-        public object Content { get; set; }
+        public object? Content { get; set; }
 
         [AssignBinding]
-        public BindingBase ItemsSource { get; set; }
+        public BindingBase? ItemsSource { get; set; }
 
-        public bool Match(object data)
+        public bool Match(object? data)
         {
             if (DataType == null)
             {
@@ -35,7 +35,7 @@ namespace Avalonia.Markup.Xaml.Templates
         }
 
         [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "If ItemsSource is a CompiledBinding, then path members will be preserver")]
-        public InstancedBinding ItemsSelector(object item)
+        public InstancedBinding? ItemsSelector(object item)
         {
             if (ItemsSource != null)
             {
@@ -52,7 +52,7 @@ namespace Avalonia.Markup.Xaml.Templates
             return null;
         }
 
-        public Control Build(object data)
+        public Control? Build(object? data)
         {
             var visualTreeForItem = TemplateContent.Load(Content)?.Control;
             if (visualTreeForItem != null)

src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/IAvaloniaXamlIlXmlNamespaceInfoProviderV1.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
     
     public class AvaloniaXamlIlXmlNamespaceInfo
     {
-        public string ClrNamespace { get; set; }
-        public string ClrAssemblyName { get; set; }
+        public string ClrNamespace { get; set; } = string.Empty;
+        public string ClrAssemblyName { get; set; } = string.Empty;
     }
 }

src/Markup/Avalonia.Markup.Xaml/XamlIl/Runtime/XamlIlRuntimeHelpers.cs

@@ -6,10 +6,7 @@ using System.Reflection;
 using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
-using Avalonia.Markup.Xaml.MarkupExtensions;
-using Avalonia.Markup.Xaml.Styling;
 using Avalonia.Platform;
-using Avalonia.Styling;
 
 // ReSharper disable UnusedMember.Global
 // ReSharper disable UnusedParameter.Global
@@ -27,9 +24,9 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
         public static Func<IServiceProvider, object> DeferredTransformationFactoryV2<T>(Func<IServiceProvider, object> builder,
             IServiceProvider provider)
         {
-            var resourceNodes = provider.GetService<IAvaloniaXamlIlParentStackProvider>().Parents
+            var resourceNodes = provider.GetRequiredService<IAvaloniaXamlIlParentStackProvider>().Parents
                 .OfType<IResourceNode>().ToList();
-            var rootObject = provider.GetService<IRootObjectProvider>().RootObject;
+            var rootObject = provider.GetRequiredService<IRootObjectProvider>().RootObject;
             var parentScope = provider.GetService<INameScope>();
             return sp =>
             {
@@ -44,17 +41,17 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
             };
         }
 
-        class DeferredParentServiceProvider :
+        private class DeferredParentServiceProvider :
             IAvaloniaXamlIlParentStackProvider,
             IServiceProvider,
             IRootObjectProvider,
             IAvaloniaXamlIlControlTemplateProvider
         {
-            private readonly IServiceProvider _parentProvider;
-            private readonly List<IResourceNode> _parentResourceNodes;
+            private readonly IServiceProvider? _parentProvider;
+            private readonly List<IResourceNode>? _parentResourceNodes;
             private readonly INameScope _nameScope;
 
-            public DeferredParentServiceProvider(IServiceProvider parentProvider, List<IResourceNode> parentResourceNodes,
+            public DeferredParentServiceProvider(IServiceProvider? parentProvider, List<IResourceNode>? parentResourceNodes,
                 object rootObject, INameScope nameScope)
             {
                 _parentProvider = parentProvider;
@@ -73,7 +70,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
                     yield return p;
             }
 
-            public object GetService(Type serviceType)
+            public object? GetService(Type serviceType)
             {
                 if (serviceType == typeof(INameScope))
                     return _nameScope;
@@ -115,25 +112,25 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
         public static IServiceProvider CreateInnerServiceProviderV1(IServiceProvider compiled)
             => new InnerServiceProvider(compiled);
 
-        class InnerServiceProvider : IServiceProvider
+        private class InnerServiceProvider : IServiceProvider
         {
             private readonly IServiceProvider _compiledProvider;
-            private XamlTypeResolver _resolver;
+            private XamlTypeResolver? _resolver;
 
             public InnerServiceProvider(IServiceProvider compiledProvider)
             {
                 _compiledProvider = compiledProvider;
             }
-            public object GetService(Type serviceType)
+            public object? GetService(Type serviceType)
             {
                 if (serviceType == typeof(IXamlTypeResolver))
-                    return _resolver ?? (_resolver = new XamlTypeResolver(
-                               _compiledProvider.GetService<IAvaloniaXamlIlXmlNamespaceInfoProvider>()));
+                    return _resolver ??= new XamlTypeResolver(
+                        _compiledProvider.GetRequiredService<IAvaloniaXamlIlXmlNamespaceInfoProvider>());
                 return null;
             }
         }
 
-        class XamlTypeResolver : IXamlTypeResolver
+        private class XamlTypeResolver : IXamlTypeResolver
         {
             private readonly IAvaloniaXamlIlXmlNamespaceInfoProvider _nsInfo;
 
@@ -148,7 +145,6 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
                 var sp = qualifiedTypeName.Split(new[] {':'}, 2);
                 var (ns, name) = sp.Length == 1 ? ("", qualifiedTypeName) : (sp[0], sp[1]);
                 var namespaces = _nsInfo.XmlNamespaces;
-                var dic = (Dictionary<string, IReadOnlyList<AvaloniaXamlIlXmlNamespaceInfo>>)namespaces;
                 if (!namespaces.TryGetValue(ns, out var lst))
                     throw new ArgumentException("Unable to resolve namespace for type " + qualifiedTypeName);
                 foreach (var entry in lst)
@@ -177,20 +173,20 @@ namespace Avalonia.Markup.Xaml.XamlIl.Runtime
         }
         #line default
 
-        class RootServiceProvider : IServiceProvider
+        private class RootServiceProvider : IServiceProvider
         {
             private readonly INameScope _nameScope;
-            private readonly IServiceProvider _parentServiceProvider;
-            private readonly IRuntimePlatform _runtimePlatform;
+            private readonly IServiceProvider? _parentServiceProvider;
+            private readonly IRuntimePlatform? _runtimePlatform;
 
-            public RootServiceProvider(INameScope nameScope, IServiceProvider parentServiceProvider)
+            public RootServiceProvider(INameScope nameScope, IServiceProvider? parentServiceProvider)
             {
                 _nameScope = nameScope;
                 _parentServiceProvider = parentServiceProvider;
                 _runtimePlatform = AvaloniaLocator.Current.GetService<IRuntimePlatform>();
             }
 
-            public object GetService(Type serviceType)
+            public object? GetService(Type serviceType)
             {
                 if (serviceType == typeof(INameScope))
                     return _nameScope;

src/Markup/Avalonia.Markup/Data/Binding.cs

@@ -16,7 +16,6 @@ namespace Avalonia.Data
         /// Initializes a new instance of the <see cref="Binding"/> class.
         /// </summary>
         public Binding()
-            :base()
         {
         }
 
@@ -54,7 +53,7 @@ namespace Avalonia.Data
         /// <summary>
         /// Gets or sets a function used to resolve types from names in the binding path.
         /// </summary>
-        public Func<string, string, Type>? TypeResolver { get; set; }
+        public Func<string?, string, Type>? TypeResolver { get; set; }
 
         private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty? targetProperty, object? anchor, bool enableDataValidation)
         {

src/Markup/Avalonia.Markup/Data/BindingBase.cs

@@ -7,7 +7,6 @@ using Avalonia.LogicalTree;
 using Avalonia.Reactive;
 using Avalonia.VisualTree;
 
-
 namespace Avalonia.Data
 {
     public abstract class BindingBase : IBinding
@@ -68,7 +67,7 @@ namespace Avalonia.Data
 
         public WeakReference? DefaultAnchor { get; set; }
 
-        public WeakReference<INameScope>? NameScope { get; set; }
+        public WeakReference<INameScope?>? NameScope { get; set; }
 
         private protected abstract ExpressionObserver CreateExpressionObserver(
             AvaloniaObject target,
@@ -169,7 +168,7 @@ namespace Avalonia.Data
         {
             _ = target ?? throw new ArgumentNullException(nameof(target));
 
-            if (NameScope is null || !NameScope.TryGetTarget(out var scope) || scope is null)
+            if (NameScope is null || !NameScope.TryGetTarget(out var scope))
                 throw new InvalidOperationException("Name scope is null or was already collected");
             var result = new ExpressionObserver(
                 NameScopeLocator.Track(scope, elementName),

src/Markup/Avalonia.Markup/Data/TemplateBinding.cs

@@ -16,7 +16,7 @@ namespace Avalonia.Data
         ISetterValue
     {
         private bool _isSetterValue;
-        private StyledElement _target = default!;
+        private StyledElement? _target;
         private Type? _targetType;
         private bool _hasProducedValue;
 
@@ -42,7 +42,7 @@ namespace Avalonia.Data
             //
             // If the binding appears in a `Setter`, then make a clone and instantiate that because
             // because the setter can outlive the control and cause a leak.
-            if (_target == null && !_isSetterValue)
+            if (_target is null && !_isSetterValue)
             {
                 _target = (StyledElement)target;
                 _targetType = targetProperty?.PropertyType;
@@ -93,9 +93,9 @@ namespace Avalonia.Data
 
         void IObserver<object?>.OnNext(object? value)
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent && Property != null)
+            if (_target?.TemplatedParent is { } templatedParent && Property is not null)
             {
-                if (Converter != null)
+                if (Converter is not null)
                 {
                     value = Converter.ConvertBack(
                         value,
@@ -114,24 +114,31 @@ namespace Avalonia.Data
         protected override void Subscribed()
         {
             TemplatedParentChanged();
-            _target.PropertyChanged += TargetPropertyChanged;
+
+            if (_target is not null)
+            {
+                _target.PropertyChanged += TargetPropertyChanged;
+            }
         }
 
         protected override void Unsubscribed()
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent)
+            if (_target?.TemplatedParent is { } templatedParent)
             {
                 templatedParent.PropertyChanged -= TemplatedParentPropertyChanged;
             }
 
-            _target.PropertyChanged -= TargetPropertyChanged;
+            if (_target is not null)
+            {
+                _target.PropertyChanged -= TargetPropertyChanged;
+            }
         }
 
         private void PublishValue()
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent)
+            if (_target?.TemplatedParent is { } templatedParent)
             {
-                var value = Property != null ?
+                var value = Property is not null ?
                     templatedParent.GetValue(Property) :
                     _target.TemplatedParent;
 
@@ -152,7 +159,7 @@ namespace Avalonia.Data
 
         private void TemplatedParentChanged()
         {
-            if (_target.TemplatedParent is AvaloniaObject templatedParent)
+            if (_target?.TemplatedParent is { } templatedParent)
             {
                 templatedParent.PropertyChanged += TemplatedParentPropertyChanged;
             }

src/Markup/Avalonia.Markup/Markup/Data/DelayedBinding.cs

@@ -20,8 +20,7 @@ namespace Avalonia.Markup.Data
     /// </remarks>
     public static class DelayedBinding
     {
-        private static ConditionalWeakTable<StyledElement, List<Entry>> _entries = 
-            new ConditionalWeakTable<StyledElement, List<Entry>>();
+        private static readonly ConditionalWeakTable<StyledElement, List<Entry>> _entries = new();
 
         /// <summary>
         /// Adds a delayed binding to a control.
@@ -57,7 +56,7 @@ namespace Avalonia.Markup.Data
         /// <param name="target">The control.</param>
         /// <param name="property">The property on the control to bind to.</param>
         /// <param name="value">A function which returns the value.</param>
-        public static void Add(StyledElement target, PropertyInfo property, Func<StyledElement, object> value)
+        public static void Add(StyledElement target, PropertyInfo property, Func<StyledElement, object?> value)
         {
             if (target.IsInitialized)
             {
@@ -126,14 +125,14 @@ namespace Avalonia.Markup.Data
 
         private class ClrPropertyValueEntry : Entry
         {
-            public ClrPropertyValueEntry(PropertyInfo property, Func<StyledElement, object> value)
+            public ClrPropertyValueEntry(PropertyInfo property, Func<StyledElement, object?> value)
             {
                 Property = property;
                 Value = value;
             }
 
             public PropertyInfo Property { get; }
-            public Func<StyledElement, object> Value { get; }
+            public Func<StyledElement, object?> Value { get; }
 
             public override void Apply(StyledElement control)
             {

src/Markup/Avalonia.Markup/Markup/Parsers/BindingExpressionGrammar.cs

@@ -6,8 +6,6 @@ using Avalonia.Utilities;
 using System;
 using System.Collections.Generic;
 
-#nullable enable
-
 namespace Avalonia.Markup.Parsers
 {
     internal enum SourceMode
@@ -201,8 +199,8 @@ namespace Avalonia.Markup.Parsers
 
             nodes.Add(new AttachedPropertyNameNode
             {
-                Namespace = ns.ToString(),
-                TypeName = owner.ToString(),
+                Namespace = ns,
+                TypeName = owner,
                 PropertyName = name.ToString()
             });
             return State.AfterMember;

src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Markup.Parsers
     internal static class ExpressionObserverBuilder
     {
         [RequiresUnreferencedCode(TrimmingMessages.ReflectionBindingRequiresUnreferencedCodeMessage)]
-        internal static (ExpressionNode Node, SourceMode Mode) Parse(string expression, bool enableValidation = false, Func<string, string, Type>? typeResolver = null,
+        internal static (ExpressionNode Node, SourceMode Mode) Parse(string expression, bool enableValidation = false, Func<string?, string, Type>? typeResolver = null,
             INameScope? nameScope = null)
         {
             if (string.IsNullOrWhiteSpace(expression))
@@ -35,7 +35,7 @@ namespace Avalonia.Markup.Parsers
             string expression,
             bool enableDataValidation = false,
             string? description = null,
-            Func<string, string, Type>? typeResolver = null)
+            Func<string?, string, Type>? typeResolver = null)
         {
             return new ExpressionObserver(
                 root,
@@ -49,7 +49,7 @@ namespace Avalonia.Markup.Parsers
             string expression,
             bool enableDataValidation = false,
             string? description = null,
-            Func<string, string, Type>? typeResolver = null)
+            Func<string?, string, Type>? typeResolver = null)
         {
             _ = rootObservable ?? throw new ArgumentNullException(nameof(rootObservable));
 
@@ -66,7 +66,7 @@ namespace Avalonia.Markup.Parsers
             IObservable<ValueTuple> update,
             bool enableDataValidation = false,
             string? description = null,
-            Func<string, string, Type>? typeResolver = null)
+            Func<string?, string, Type>? typeResolver = null)
         {
             _ = rootGetter ?? throw new ArgumentNullException(nameof(rootGetter));
 

src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionParser.cs

@@ -2,8 +2,6 @@ using Avalonia.Data.Core;
 using Avalonia.Markup.Parsers.Nodes;
 using Avalonia.Utilities;
 using System;
-using System.Collections.Generic;
-using System.Linq;
 using Avalonia.Controls;
 using System.Diagnostics.CodeAnalysis;
 
@@ -18,7 +16,7 @@ namespace Avalonia.Markup.Parsers
         private readonly Func<string, string, Type>? _typeResolver;
         private readonly INameScope? _nameScope;
 
-        public ExpressionParser(bool enableValidation, Func<string, string, Type>? typeResolver, INameScope? nameScope)
+        public ExpressionParser(bool enableValidation, Func<string?, string, Type>? typeResolver, INameScope? nameScope)
         {
             _typeResolver = typeResolver;
             _nameScope = nameScope;
@@ -37,13 +35,13 @@ namespace Avalonia.Markup.Parsers
                 ExpressionNode? nextNode = null;
                 switch (astNode)
                 {
-                    case BindingExpressionGrammar.EmptyExpressionNode _:
+                    case BindingExpressionGrammar.EmptyExpressionNode:
                         nextNode = new EmptyExpressionNode();
                         break;
-                    case BindingExpressionGrammar.NotNode _:
+                    case BindingExpressionGrammar.NotNode:
                         nextNode = new LogicalNotNode();
                         break;
-                    case BindingExpressionGrammar.StreamNode _:
+                    case BindingExpressionGrammar.StreamNode:
                         nextNode = new StreamNode();
                         break;
                     case BindingExpressionGrammar.PropertyNameNode propName:
@@ -55,7 +53,7 @@ namespace Avalonia.Markup.Parsers
                     case BindingExpressionGrammar.AttachedPropertyNameNode attachedProp:
                         nextNode = ParseAttachedProperty(attachedProp);
                         break;
-                    case BindingExpressionGrammar.SelfNode _:
+                    case BindingExpressionGrammar.SelfNode:
                         nextNode = new SelfNode();
                         break;
                     case BindingExpressionGrammar.AncestorNode ancestor:

src/Markup/Avalonia.Markup/Markup/Parsers/SelectorGrammar.cs

@@ -4,9 +4,7 @@ using System.Linq;
 using Avalonia.Data.Core;
 using Avalonia.Utilities;
 
-#nullable enable
-
-// Don't need to override GetHashCode as the ISyntax objects will not be stored in a hash; the 
+// Don't need to override GetHashCode as the ISyntax objects will not be stored in a hash; the
 // only reason they have overridden Equals methods is for unit testing.
 #pragma warning disable 659
 
@@ -642,7 +640,7 @@ namespace Avalonia.Markup.Parsers
         {
             public override bool Equals(object? obj)
             {
-                return obj is CommaSyntax or;
+                return obj is CommaSyntax;
             }
         }
 

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/ControlTemplateTests.cs

@@ -2,6 +2,7 @@ using System;
 using System.Linq;
 using Avalonia.Controls;
 using Avalonia.Controls.Presenters;
+using Avalonia.Controls.Primitives;
 using Avalonia.Data;
 using Avalonia.Diagnostics;
 using Avalonia.Markup.Xaml.Templates;
@@ -308,6 +309,16 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             Assert.Equal("Foo", foo.Name);
             Assert.Equal("Bar", bar.Name);
         }
+
+        [Fact]
+        public void ControlTemplate_Can_Be_Empty()
+        {
+            var xaml = "<ControlTemplate xmlns='https://github.com/avaloniaui' />";
+            var template = AvaloniaRuntimeXamlLoader.Parse<ControlTemplate>(xaml);
+
+            var templateResult = template.Build(new TemplatedControl());
+            Assert.Null(templateResult);
+        }
     }
     public class ListBoxHierarchyLine : Panel
     {