Fixed ItemContainerGenerator usages.

src/Avalonia.Controls/ComboBox.cs

@@ -360,12 +360,12 @@ namespace Avalonia.Controls
             var selectedIndex = SelectedIndex;
             if (IsDropDownOpen && selectedIndex != -1)
             {
-                var container = ItemContainerGenerator!.ContainerFromIndex(selectedIndex);
+                var container = ItemContainerGenerator.ContainerFromIndex(selectedIndex);
 
                 if (container == null && SelectedIndex != -1)
                 {
                     ScrollIntoView(Selection.SelectedIndex);
-                    container = ItemContainerGenerator!.ContainerFromIndex(selectedIndex);
+                    container = ItemContainerGenerator.ContainerFromIndex(selectedIndex);
                 }
 
                 if (container != null && CanFocus(container))
@@ -415,7 +415,7 @@ namespace Avalonia.Controls
 
         private void SelectFocusedItem()
         {
-            foreach (ItemContainerInfo dropdownItem in ItemContainerGenerator!.Containers)
+            foreach (ItemContainerInfo dropdownItem in ItemContainerGenerator.Containers)
             {
                 if (dropdownItem.ContainerControl.IsFocused)
                 {

src/Avalonia.Controls/MenuBase.cs

@@ -81,13 +81,13 @@ namespace Avalonia.Controls
             {
                 var index = SelectedIndex;
                 return (index != -1) ?
-                    (IMenuItem?)ItemContainerGenerator!.ContainerFromIndex(index) :
+                    (IMenuItem?)ItemContainerGenerator.ContainerFromIndex(index) :
                     null;
             }
             set
             {
                 SelectedIndex = value is not null ?
-                    ItemContainerGenerator!.IndexFromContainer(value) : -1;
+                    ItemContainerGenerator.IndexFromContainer(value) : -1;
             }
         }
 
@@ -96,7 +96,7 @@ namespace Avalonia.Controls
         {
             get
             {
-                return ItemContainerGenerator!.Containers
+                return ItemContainerGenerator.Containers
                     .Select(x => x.ContainerControl)
                     .OfType<IMenuItem>();
             }

src/Avalonia.Controls/MenuItem.cs

@@ -308,12 +308,12 @@ namespace Avalonia.Controls
             {
                 var index = SelectedIndex;
                 return (index != -1) ?
-                    (IMenuItem?)ItemContainerGenerator!.ContainerFromIndex(index) :
+                    (IMenuItem?)ItemContainerGenerator.ContainerFromIndex(index) :
                     null;
             }
             set
             {
-                SelectedIndex = value is not null ? ItemContainerGenerator!.IndexFromContainer(value) : -1;
+                SelectedIndex = value is not null ? ItemContainerGenerator.IndexFromContainer(value) : -1;
             }
         }
 
@@ -322,7 +322,7 @@ namespace Avalonia.Controls
         {
             get
             {
-                return ItemContainerGenerator!.Containers
+                return ItemContainerGenerator.Containers
                     .Select(x => x.ContainerControl)
                     .OfType<IMenuItem>();
             }

src/Avalonia.Controls/Presenters/CarouselPresenter.cs

@@ -170,7 +170,7 @@ namespace Avalonia.Controls.Presenters
         {
             if (fromIndex != toIndex)
             {
-                var generator = ItemContainerGenerator!;
+                var generator = ItemContainerGenerator;
                 IControl? from = null;
                 IControl? to = null;
 

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -908,7 +908,7 @@ namespace Avalonia.Controls.Primitives
                 {
                     MarkContainerSelected(
                         container,
-                        Selection.IsSelected(ItemContainerGenerator!.IndexFromContainer(container)));
+                        Selection.IsSelected(ItemContainerGenerator.IndexFromContainer(container)));
                 }
             }
         }

src/Avalonia.Controls/TabControl.cs

@@ -164,7 +164,7 @@ namespace Avalonia.Controls
             else
             {
                 var container = SelectedItem as IContentControl ??
-                    ItemContainerGenerator!.ContainerFromIndex(SelectedIndex) as IContentControl;
+                    ItemContainerGenerator.ContainerFromIndex(SelectedIndex) as IContentControl;
                 SelectedContentTemplate = container?.ContentTemplate;
                 SelectedContent = container?.Content;
             }

src/Avalonia.Controls/TreeView.cs

@@ -79,7 +79,7 @@ namespace Avalonia.Controls
         /// Gets the <see cref="ITreeItemContainerGenerator"/> for the tree view.
         /// </summary>
         public new ITreeItemContainerGenerator ItemContainerGenerator =>
-            (ITreeItemContainerGenerator)base.ItemContainerGenerator!;
+            (ITreeItemContainerGenerator)base.ItemContainerGenerator;
 
         /// <summary>
         /// Gets or sets a value indicating whether to automatically scroll to newly selected items.

src/Avalonia.Controls/TreeViewItem.cs

@@ -89,7 +89,7 @@ namespace Avalonia.Controls
         /// Gets the <see cref="ITreeItemContainerGenerator"/> for the tree view.
         /// </summary>
         public new ITreeItemContainerGenerator ItemContainerGenerator =>
-            (ITreeItemContainerGenerator)base.ItemContainerGenerator!;
+            (ITreeItemContainerGenerator)base.ItemContainerGenerator;
 
         /// <inheritdoc/>
         protected override IItemContainerGenerator CreateItemContainerGenerator() => CreateTreeItemContainerGenerator<TreeViewItem>();