diff --git a/src/Avalonia.Controls/Automation/AutomationPropertyChangedEventArgs.cs b/src/Avalonia.Controls/Automation/AutomationPropertyChangedEventArgs.cs
index b8018613f8..3b7eb70fcb 100644
--- a/src/Avalonia.Controls/Automation/AutomationPropertyChangedEventArgs.cs
+++ b/src/Avalonia.Controls/Automation/AutomationPropertyChangedEventArgs.cs
@@ -1,7 +1,5 @@
 using System;
 
-#nullable enable
-
 namespace Avalonia.Automation
 {
     public class AutomationPropertyChangedEventArgs : EventArgs
diff --git a/src/Avalonia.Controls/Automation/Peers/AutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/AutomationPeer.cs
index 54b2fcc7fa..71421ac136 100644
--- a/src/Avalonia.Controls/Automation/Peers/AutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/AutomationPeer.cs
@@ -1,8 +1,6 @@
 using System;
 using System.Collections.Generic;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public enum AutomationControlType
diff --git a/src/Avalonia.Controls/Automation/Peers/ButtonAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ButtonAutomationPeer.cs
index f5d6dce039..4ac07717da 100644
--- a/src/Avalonia.Controls/Automation/Peers/ButtonAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ButtonAutomationPeer.cs
@@ -1,8 +1,6 @@
 using Avalonia.Automation.Provider;
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class ButtonAutomationPeer : ContentControlAutomationPeer,
diff --git a/src/Avalonia.Controls/Automation/Peers/ComboBoxAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ComboBoxAutomationPeer.cs
index 0122527950..5ff291d972 100644
--- a/src/Avalonia.Controls/Automation/Peers/ComboBoxAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ComboBoxAutomationPeer.cs
@@ -3,8 +3,6 @@ using System.Collections.Generic;
 using Avalonia.Automation.Provider;
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class ComboBoxAutomationPeer : SelectingItemsControlAutomationPeer,
@@ -60,7 +58,7 @@ namespace Avalonia.Automation.Peers
             return null;
         }
 
-        protected override void OwnerPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e)
+        protected override void OwnerPropertyChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
         {
             base.OwnerPropertyChanged(sender, e);
 
diff --git a/src/Avalonia.Controls/Automation/Peers/ContentControlAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ContentControlAutomationPeer.cs
index 08e4f2a926..df24222a0c 100644
--- a/src/Avalonia.Controls/Automation/Peers/ContentControlAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ContentControlAutomationPeer.cs
@@ -1,7 +1,5 @@
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class ContentControlAutomationPeer : ControlAutomationPeer
diff --git a/src/Avalonia.Controls/Automation/Peers/ControlAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ControlAutomationPeer.cs
index f7a993e16b..28cb3e34b2 100644
--- a/src/Avalonia.Controls/Automation/Peers/ControlAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ControlAutomationPeer.cs
@@ -4,8 +4,6 @@ using System.Linq;
 using Avalonia.Controls;
 using Avalonia.VisualTree;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     /// <summary>
@@ -174,9 +172,9 @@ namespace Avalonia.Automation.Peers
             visualChildren.CollectionChanged += VisualChildrenChanged;
         }
 
-        private void VisualChildrenChanged(object sender, EventArgs e) => InvalidateChildren();
+        private void VisualChildrenChanged(object? sender, EventArgs e) => InvalidateChildren();
 
-        private void OwnerPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e)
+        private void OwnerPropertyChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
         {
             if (e.Property == Visual.IsVisibleProperty)
             {
diff --git a/src/Avalonia.Controls/Automation/Peers/ItemsControlAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ItemsControlAutomationPeer.cs
index 0d35920e19..db16bf0a53 100644
--- a/src/Avalonia.Controls/Automation/Peers/ItemsControlAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ItemsControlAutomationPeer.cs
@@ -1,8 +1,6 @@
 using Avalonia.Automation.Provider;
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class ItemsControlAutomationPeer : ControlAutomationPeer, IScrollProvider
diff --git a/src/Avalonia.Controls/Automation/Peers/ListItemAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ListItemAutomationPeer.cs
index 0621e81c1a..ac23873e6a 100644
--- a/src/Avalonia.Controls/Automation/Peers/ListItemAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ListItemAutomationPeer.cs
@@ -4,8 +4,6 @@ using Avalonia.Controls;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Selection;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class ListItemAutomationPeer : ContentControlAutomationPeer,
diff --git a/src/Avalonia.Controls/Automation/Peers/MenuItemAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/MenuItemAutomationPeer.cs
index 1994f004d6..c98c5c9a22 100644
--- a/src/Avalonia.Controls/Automation/Peers/MenuItemAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/MenuItemAutomationPeer.cs
@@ -1,8 +1,6 @@
 using Avalonia.Controls;
 using Avalonia.Controls.Primitives;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class MenuItemAutomationPeer : ControlAutomationPeer
diff --git a/src/Avalonia.Controls/Automation/Peers/NoneAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/NoneAutomationPeer.cs
index a995886179..0f92fed6f3 100644
--- a/src/Avalonia.Controls/Automation/Peers/NoneAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/NoneAutomationPeer.cs
@@ -1,7 +1,5 @@
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     /// <summary>
diff --git a/src/Avalonia.Controls/Automation/Peers/PopupAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/PopupAutomationPeer.cs
index 9c24f855f8..25f6ca6e2d 100644
--- a/src/Avalonia.Controls/Automation/Peers/PopupAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/PopupAutomationPeer.cs
@@ -4,8 +4,6 @@ using Avalonia.Controls;
 using Avalonia.Controls.Diagnostics;
 using Avalonia.Controls.Primitives;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class PopupAutomationPeer : ControlAutomationPeer
@@ -26,7 +24,7 @@ namespace Avalonia.Automation.Peers
         protected override bool IsContentElementCore() => false;
         protected override bool IsControlElementCore() => false;
 
-        private void PopupOpenedClosed(object sender, EventArgs e)
+        private void PopupOpenedClosed(object? sender, EventArgs e)
         {
             // This is golden. We're following WPF's automation peer API here where the
             // parent of a peer is set when another peer returns it as a child. We want to
diff --git a/src/Avalonia.Controls/Automation/Peers/PopupRootAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/PopupRootAutomationPeer.cs
index fb717ef98b..cb65682c06 100644
--- a/src/Avalonia.Controls/Automation/Peers/PopupRootAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/PopupRootAutomationPeer.cs
@@ -1,8 +1,6 @@
 using System;
 using Avalonia.Controls.Primitives;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class PopupRootAutomationPeer : WindowBaseAutomationPeer
@@ -27,13 +25,13 @@ namespace Avalonia.Automation.Peers
             return parent;
         }
 
-        private void OnOpened(object sender, EventArgs e)
+        private void OnOpened(object? sender, EventArgs e)
         {
             ((PopupRoot)Owner).Opened -= OnOpened;
             StartTrackingFocus();
         }
 
-        private void OnClosed(object sender, EventArgs e)
+        private void OnClosed(object? sender, EventArgs e)
         {
             ((PopupRoot)Owner).Closed -= OnClosed;
             StopTrackingFocus();
diff --git a/src/Avalonia.Controls/Automation/Peers/RangeBaseAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/RangeBaseAutomationPeer.cs
index 1bb487b161..39398933fa 100644
--- a/src/Avalonia.Controls/Automation/Peers/RangeBaseAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/RangeBaseAutomationPeer.cs
@@ -1,8 +1,6 @@
 using Avalonia.Automation.Provider;
 using Avalonia.Controls.Primitives;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public abstract class RangeBaseAutomationPeer : ControlAutomationPeer, IRangeValueProvider
@@ -23,7 +21,7 @@ namespace Avalonia.Automation.Peers
         
         public void SetValue(double value) => Owner.Value = value;
 
-        protected virtual void OwnerPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e)
+        protected virtual void OwnerPropertyChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
         {
             if (e.Property == RangeBase.MinimumProperty)
                 RaisePropertyChangedEvent(RangeValuePatternIdentifiers.MinimumProperty, e.OldValue, e.NewValue);
diff --git a/src/Avalonia.Controls/Automation/Peers/ScrollViewerAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ScrollViewerAutomationPeer.cs
index c2474bb9b8..835ed1c4af 100644
--- a/src/Avalonia.Controls/Automation/Peers/ScrollViewerAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ScrollViewerAutomationPeer.cs
@@ -3,8 +3,6 @@ using Avalonia.Automation.Provider;
 using Avalonia.Controls;
 using Avalonia.Utilities;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class ScrollViewerAutomationPeer : ControlAutomationPeer, IScrollProvider
diff --git a/src/Avalonia.Controls/Automation/Peers/SelectingItemsControlAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/SelectingItemsControlAutomationPeer.cs
index f372e3b781..4626e30ff1 100644
--- a/src/Avalonia.Controls/Automation/Peers/SelectingItemsControlAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/SelectingItemsControlAutomationPeer.cs
@@ -6,8 +6,6 @@ using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Selection;
 using Avalonia.VisualTree;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public abstract class SelectingItemsControlAutomationPeer : ItemsControlAutomationPeer,
@@ -62,7 +60,7 @@ namespace Avalonia.Automation.Peers
             return (Owner as SelectingItemsControl)?.GetValue(ListBox.SelectionModeProperty) ?? SelectionMode.Single;
         }
 
-        protected virtual void OwnerPropertyChanged(object sender, AvaloniaPropertyChangedEventArgs e)
+        protected virtual void OwnerPropertyChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
         {
             if (e.Property == ListBox.SelectionProperty)
             {
@@ -73,7 +71,7 @@ namespace Avalonia.Automation.Peers
             }
         }
 
-        protected virtual void OwnerSelectionChanged(object sender, SelectionModelSelectionChangedEventArgs e)
+        protected virtual void OwnerSelectionChanged(object? sender, SelectionModelSelectionChangedEventArgs e)
         {
             RaiseSelectionChanged();
         }
diff --git a/src/Avalonia.Controls/Automation/Peers/TextBlockAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/TextBlockAutomationPeer.cs
index 37eaf6f7c0..8a89e38f62 100644
--- a/src/Avalonia.Controls/Automation/Peers/TextBlockAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/TextBlockAutomationPeer.cs
@@ -1,7 +1,5 @@
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class TextBlockAutomationPeer : ControlAutomationPeer
diff --git a/src/Avalonia.Controls/Automation/Peers/TextBoxAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/TextBoxAutomationPeer.cs
index 33b2ba58b6..9be17afa8c 100644
--- a/src/Avalonia.Controls/Automation/Peers/TextBoxAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/TextBoxAutomationPeer.cs
@@ -1,8 +1,6 @@
 using Avalonia.Automation.Provider;
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class TextBoxAutomationPeer : ControlAutomationPeer, IValueProvider
diff --git a/src/Avalonia.Controls/Automation/Peers/ToggleButtonAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/ToggleButtonAutomationPeer.cs
index dd0c506d29..979d54f48e 100644
--- a/src/Avalonia.Controls/Automation/Peers/ToggleButtonAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/ToggleButtonAutomationPeer.cs
@@ -1,8 +1,6 @@
 using Avalonia.Automation.Provider;
 using Avalonia.Controls.Primitives;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class ToggleButtonAutomationPeer : ContentControlAutomationPeer, IToggleProvider
diff --git a/src/Avalonia.Controls/Automation/Peers/UnrealizedElementAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/UnrealizedElementAutomationPeer.cs
index b388f21a17..56d5aa79ae 100644
--- a/src/Avalonia.Controls/Automation/Peers/UnrealizedElementAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/UnrealizedElementAutomationPeer.cs
@@ -1,8 +1,6 @@
 using System;
 using System.Collections.Generic;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     /// <summary>
diff --git a/src/Avalonia.Controls/Automation/Peers/WindowAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/WindowAutomationPeer.cs
index fbc6e9d4f4..1162132d54 100644
--- a/src/Avalonia.Controls/Automation/Peers/WindowAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/WindowAutomationPeer.cs
@@ -1,8 +1,6 @@
 using System;
 using Avalonia.Controls;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class WindowAutomationPeer : WindowBaseAutomationPeer
@@ -19,15 +17,15 @@ namespace Avalonia.Automation.Peers
 
         public new Window Owner => (Window)base.Owner;
 
-        protected override string GetNameCore() => Owner.Title;
+        protected override string? GetNameCore() => Owner.Title;
 
-        private void OnOpened(object sender, EventArgs e)
+        private void OnOpened(object? sender, EventArgs e)
         {
             Owner.Opened -= OnOpened;
             StartTrackingFocus();
         }
 
-        private void OnClosed(object sender, EventArgs e)
+        private void OnClosed(object? sender, EventArgs e)
         {
             Owner.Closed -= OnClosed;
             StopTrackingFocus();
diff --git a/src/Avalonia.Controls/Automation/Peers/WindowBaseAutomationPeer.cs b/src/Avalonia.Controls/Automation/Peers/WindowBaseAutomationPeer.cs
index b24685929a..30b56bbd96 100644
--- a/src/Avalonia.Controls/Automation/Peers/WindowBaseAutomationPeer.cs
+++ b/src/Avalonia.Controls/Automation/Peers/WindowBaseAutomationPeer.cs
@@ -6,8 +6,6 @@ using Avalonia.Input;
 using Avalonia.Platform;
 using Avalonia.VisualTree;
 
-#nullable enable
-
 namespace Avalonia.Automation.Peers
 {
     public class WindowBaseAutomationPeer : ControlAutomationPeer, IRootProvider
@@ -20,7 +18,7 @@ namespace Avalonia.Automation.Peers
         }
 
         public new WindowBase Owner => (WindowBase)base.Owner;
-        public ITopLevelImpl PlatformImpl => Owner.PlatformImpl;
+        public ITopLevelImpl? PlatformImpl => Owner.PlatformImpl;
 
         public event EventHandler? FocusChanged;
 
@@ -39,13 +37,17 @@ namespace Avalonia.Automation.Peers
 
         protected void StartTrackingFocus()
         {
-            KeyboardDevice.Instance.PropertyChanged += KeyboardDevicePropertyChanged;
-            OnFocusChanged(KeyboardDevice.Instance.FocusedElement);
+            if (KeyboardDevice.Instance is not null)
+            {
+                KeyboardDevice.Instance.PropertyChanged += KeyboardDevicePropertyChanged;
+                OnFocusChanged(KeyboardDevice.Instance.FocusedElement);
+            }
         }
 
         protected void StopTrackingFocus()
         {
-            KeyboardDevice.Instance.PropertyChanged -= KeyboardDevicePropertyChanged;
+            if (KeyboardDevice.Instance is not null)
+                KeyboardDevice.Instance.PropertyChanged -= KeyboardDevicePropertyChanged;
         }
 
         private void OnFocusChanged(IInputElement? focus)
@@ -63,11 +65,11 @@ namespace Avalonia.Automation.Peers
             }
         }
 
-        private void KeyboardDevicePropertyChanged(object sender, PropertyChangedEventArgs e)
+        private void KeyboardDevicePropertyChanged(object? sender, PropertyChangedEventArgs e)
         {
             if (e.PropertyName == nameof(KeyboardDevice.FocusedElement))
             {
-                OnFocusChanged(KeyboardDevice.Instance.FocusedElement);
+                OnFocusChanged(KeyboardDevice.Instance!.FocusedElement);
             }
         }
     }
diff --git a/src/Avalonia.Controls/Automation/Provider/IRangeValueProvider.cs b/src/Avalonia.Controls/Automation/Provider/IRangeValueProvider.cs
index d494e068f7..43a877a21a 100644
--- a/src/Avalonia.Controls/Automation/Provider/IRangeValueProvider.cs
+++ b/src/Avalonia.Controls/Automation/Provider/IRangeValueProvider.cs
@@ -1,6 +1,4 @@
-#nullable enable
-
-namespace Avalonia.Automation.Provider
+namespace Avalonia.Automation.Provider
 {
     /// <summary>
     /// Exposes methods and properties to support access by a UI Automation client to controls
diff --git a/src/Avalonia.Controls/Automation/Provider/IRootProvider.cs b/src/Avalonia.Controls/Automation/Provider/IRootProvider.cs
index 8ea53863eb..ce38059559 100644
--- a/src/Avalonia.Controls/Automation/Provider/IRootProvider.cs
+++ b/src/Avalonia.Controls/Automation/Provider/IRootProvider.cs
@@ -2,8 +2,6 @@
 using Avalonia.Automation.Peers;
 using Avalonia.Platform;
 
-#nullable enable
-
 namespace Avalonia.Automation.Provider
 {
     public interface IRootProvider
diff --git a/src/Avalonia.Controls/Automation/Provider/ISelectionItemProvider .cs b/src/Avalonia.Controls/Automation/Provider/ISelectionItemProvider .cs
index 767d6bd7a2..6cea1d1350 100644
--- a/src/Avalonia.Controls/Automation/Provider/ISelectionItemProvider .cs	
+++ b/src/Avalonia.Controls/Automation/Provider/ISelectionItemProvider .cs	
@@ -1,6 +1,4 @@
-#nullable enable
-
-namespace Avalonia.Automation.Provider
+namespace Avalonia.Automation.Provider
 {
     /// <summary>
     /// Exposes methods and properties to support access by a UI Automation client to individual,
diff --git a/src/Avalonia.Controls/Automation/Provider/IValueProvider.cs b/src/Avalonia.Controls/Automation/Provider/IValueProvider.cs
index 83dbde4ec2..e025e28782 100644
--- a/src/Avalonia.Controls/Automation/Provider/IValueProvider.cs
+++ b/src/Avalonia.Controls/Automation/Provider/IValueProvider.cs
@@ -1,6 +1,4 @@
-#nullable enable
-
-namespace Avalonia.Automation.Provider
+namespace Avalonia.Automation.Provider
 {
     /// <summary>
     /// Exposes methods and properties to support access by a UI Automation client to controls