diff --git a/src/Avalonia.Controls/Control.cs b/src/Avalonia.Controls/Control.cs
index 41370d8464..620f5afa81 100644
--- a/src/Avalonia.Controls/Control.cs
+++ b/src/Avalonia.Controls/Control.cs
@@ -8,6 +8,8 @@ using Avalonia.Rendering;
 using Avalonia.Styling;
 using Avalonia.VisualTree;
 
+#nullable enable
+
 namespace Avalonia.Controls
 {
     /// <summary>
@@ -23,20 +25,20 @@ namespace Avalonia.Controls
         /// <summary>
         /// Defines the <see cref="FocusAdorner"/> property.
         /// </summary>
-        public static readonly StyledProperty<ITemplate<IControl>> FocusAdornerProperty =
-            AvaloniaProperty.Register<Control, ITemplate<IControl>>(nameof(FocusAdorner));
+        public static readonly StyledProperty<ITemplate<IControl>?> FocusAdornerProperty =
+            AvaloniaProperty.Register<Control, ITemplate<IControl>?>(nameof(FocusAdorner));
 
         /// <summary>
         /// Defines the <see cref="Tag"/> property.
         /// </summary>
-        public static readonly StyledProperty<object> TagProperty =
-            AvaloniaProperty.Register<Control, object>(nameof(Tag));
+        public static readonly StyledProperty<object?> TagProperty =
+            AvaloniaProperty.Register<Control, object?>(nameof(Tag));
         
         /// <summary>
         /// Defines the <see cref="ContextMenu"/> property.
         /// </summary>
-        public static readonly StyledProperty<ContextMenu> ContextMenuProperty =
-            AvaloniaProperty.Register<Control, ContextMenu>(nameof(ContextMenu));
+        public static readonly StyledProperty<ContextMenu?> ContextMenuProperty =
+            AvaloniaProperty.Register<Control, ContextMenu?>(nameof(ContextMenu));
 
         /// <summary>
         /// Event raised when an element wishes to be scrolled into view.
@@ -44,16 +46,16 @@ namespace Avalonia.Controls
         public static readonly RoutedEvent<RequestBringIntoViewEventArgs> RequestBringIntoViewEvent =
             RoutedEvent.Register<Control, RequestBringIntoViewEventArgs>("RequestBringIntoView", RoutingStrategies.Bubble);
 
-        private DataTemplates _dataTemplates;
-        private IControl _focusAdorner;
+        private DataTemplates? _dataTemplates;
+        private IControl? _focusAdorner;
 
         /// <summary>
         /// Gets or sets the control's focus adorner.
         /// </summary>
-        public ITemplate<IControl> FocusAdorner
+        public ITemplate<IControl>? FocusAdorner
         {
-            get { return GetValue(FocusAdornerProperty); }
-            set { SetValue(FocusAdornerProperty, value); }
+            get => GetValue(FocusAdornerProperty);
+            set => SetValue(FocusAdornerProperty, value);
         }
 
         /// <summary>
@@ -63,27 +65,27 @@ namespace Avalonia.Controls
         /// Each control may define data templates which are applied to the control itself and its
         /// children.
         /// </remarks>
-        public DataTemplates DataTemplates => _dataTemplates ?? (_dataTemplates = new DataTemplates());
+        public DataTemplates DataTemplates => _dataTemplates ??= new DataTemplates();
 
         /// <summary>
         /// Gets or sets a context menu to the control.
         /// </summary>
-        public ContextMenu ContextMenu
+        public ContextMenu? ContextMenu
         {
-            get { return GetValue(ContextMenuProperty); }
-            set { SetValue(ContextMenuProperty, value); }
+            get => GetValue(ContextMenuProperty);
+            set => SetValue(ContextMenuProperty, value);
         }
 
         /// <summary>
         /// Gets or sets a user-defined object attached to the control.
         /// </summary>
-        public object Tag
+        public object? Tag
         {
-            get { return GetValue(TagProperty); }
-            set { SetValue(TagProperty, value); }
+            get => GetValue(TagProperty);
+            set => SetValue(TagProperty, value);
         }
 
-        public new IControl Parent => (IControl)base.Parent;
+        public new IControl? Parent => (IControl?)base.Parent;
 
         /// <inheritdoc/>
         bool IDataTemplateHost.IsDataTemplatesInitialized => _dataTemplates != null;
@@ -106,15 +108,10 @@ namespace Avalonia.Controls
                     {
                         var c = i as IControl;
 
-                        if (c?.IsInitialized == false)
+                        if (c?.IsInitialized == false && c is ISupportInitialize init)
                         {
-                            var init = c as ISupportInitialize;
-
-                            if (init != null)
-                            {
-                                init.BeginInit();
-                                init.EndInit();
-                            }
+                            init.BeginInit();
+                            init.EndInit();
                         }
                     }
                 }
@@ -131,10 +128,7 @@ namespace Avalonia.Controls
         /// Gets the element that receives the focus adorner.
         /// </summary>
         /// <returns>The control that receives the focus adorner.</returns>
-        protected virtual IControl GetTemplateFocusTarget()
-        {
-            return this;
-        }
+        protected virtual IControl? GetTemplateFocusTarget() => this;
 
         /// <inheritdoc/>
         protected sealed override void OnAttachedToVisualTreeCore(VisualTreeAttachmentEventArgs e)
@@ -173,15 +167,10 @@ namespace Avalonia.Controls
                         }
                     }
 
-                    if (_focusAdorner != null)
+                    if (_focusAdorner != null && GetTemplateFocusTarget() is Visual target)
                     {
-                        var target = (Visual)GetTemplateFocusTarget();
-
-                        if (target != null)
-                        {
-                            AdornerLayer.SetAdornedElement((Visual)_focusAdorner, target);
-                            adornerLayer.Children.Add(_focusAdorner);
-                        }
+                        AdornerLayer.SetAdornedElement((Visual)_focusAdorner, target);
+                        adornerLayer.Children.Add(_focusAdorner);
                     }
                 }
             }
diff --git a/src/Avalonia.Visuals/Visual.cs b/src/Avalonia.Visuals/Visual.cs
index 9327531b46..80d4195421 100644
--- a/src/Avalonia.Visuals/Visual.cs
+++ b/src/Avalonia.Visuals/Visual.cs
@@ -150,7 +150,7 @@ namespace Avalonia
         public TransformedBounds? TransformedBounds => _transformedBounds;
 
         /// <summary>
-        /// Gets a value indicating whether the control should be clipped to its bounds.
+        /// Gets or sets a value indicating whether the control should be clipped to its bounds.
         /// </summary>
         public bool ClipToBounds
         {
@@ -191,7 +191,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets a value indicating whether this control is visible.
+        /// Gets or sets a value indicating whether this control is visible.
         /// </summary>
         public bool IsVisible
         {
@@ -200,7 +200,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets the opacity of the control.
+        /// Gets or sets the opacity of the control.
         /// </summary>
         public double Opacity
         {
@@ -209,7 +209,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets the opacity mask of the control.
+        /// Gets or sets the opacity mask of the control.
         /// </summary>
         public IBrush OpacityMask
         {
@@ -218,7 +218,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets the render transform of the control.
+        /// Gets or sets the render transform of the control.
         /// </summary>
         public ITransform RenderTransform
         {
@@ -227,7 +227,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets the transform origin of the control.
+        /// Gets or sets the transform origin of the control.
         /// </summary>
         public RelativePoint RenderTransformOrigin
         {
@@ -236,7 +236,7 @@ namespace Avalonia
         }
 
         /// <summary>
-        /// Gets the Z index of the control.
+        /// Gets or sets the Z index of the control.
         /// </summary>
         /// <remarks>
         /// Controls with a higher <see cref="ZIndex"/> will appear in front of controls with