fixed code to be nullable safe

Author: pictos

src/CommunityToolkit/Xamarin.CommunityToolkit.UnitTests/Behaviors/SetFocusOnEntryCompleted_Tests.cs

@@ -36,7 +36,7 @@ public void SetsFocusWhenCompleted()
 			Assert.True(entry2.IsFocused);
 		}
 
-		public Entry CreateEntry(VisualElement nextElement = null)
+		public Entry CreateEntry(VisualElement? nextElement = null)
 		{
 			var entry = new Entry();
 

src/CommunityToolkit/Xamarin.CommunityToolkit/Behaviors/AttachedBehaviors/SetFocusOnEntryCompletedBehavior.shared.cs

@@ -42,14 +42,13 @@ static void OnNextElementChanged(BindableObject bindable, object oldValue, objec
 			var weakEntry = new WeakReference<Entry>(entry);
 			entry.Completed += completedHandler;
 
-			void completedHandler(object sender, EventArgs e)
+			void completedHandler(object? sender, EventArgs e)
 			{
 				if (weakEntry.TryGetTarget(out var origEntry))
 				{
 					GetNextElement(origEntry)?.Focus();
 				}
 			}
 		}
-
 	}
 }