Review suggestions apply

src/Avalonia.Base/Data/BindingValue.cs

@@ -247,7 +247,7 @@ namespace Avalonia.Data
                 UnsetValueType _ => Unset,
                 DoNothingType _ => DoNothing,
                 BindingNotification n => n.ToBindingValue().Cast<T>(),
-                _ => new BindingValue<T>((T)value!)
+                _ => new BindingValue<T>((T?)value)
             };
         }
 

src/Avalonia.Base/PropertyStore/ConstantValueEntry.cs

@@ -30,7 +30,7 @@ namespace Avalonia.PropertyStore
             IValueSink sink)
         {
             Property = property;
-            _value = value!;
+            _value = value;
             Priority = priority;
             _sink = sink;
         }

src/Avalonia.Base/ValueStore.cs

@@ -192,7 +192,7 @@ namespace Avalonia
                         _values.SetValue(property, sentinel);
                     }
 
-                    NotifyValueChanged<T>(property, old!, default!, BindingPriority.Unset);
+                    NotifyValueChanged<T>(property, old, default, BindingPriority.Unset);
                 }
             }
         }