Add a way to reset an IBrush to null for default functionality.

Source/Editor/CustomEditors/Editors/IBrushEditor.cs

@@ -16,6 +16,7 @@ namespace FlaxEditor.CustomEditors.Editors
         /// <inheritdoc />
         protected override OptionType[] Options => new[]
         {
+            new OptionType("null", null),
             new OptionType("Texture", typeof(TextureBrush)),
             new OptionType("Sprite", typeof(SpriteBrush)),
             new OptionType("GPU Texture", typeof(GPUTextureBrush)),

Source/Editor/CustomEditors/Editors/ObjectSwitcherEditor.cs

@@ -158,7 +158,9 @@ namespace FlaxEditor.CustomEditors.Editors
             if (comboBox.SelectedIndex != -1)
             {
                 var option = _options[comboBox.SelectedIndex];
-                value = option.Creator(option.Type);
+                if (option.Type != null)
+                    value = option.Creator(option.Type);
+
             }
             SetValue(value);
             RebuildLayoutOnRefresh();