[Presentation] Fix issue with binding quantum nodes when associated n…

…ame is not found (#2195)

Note: the solution is rather hackish at the moment. To be revisited once we have an Avalonia version.
Should we then introduce a service for setting/retrieving the Unset value

sources/editor/Stride.Core.Assets.Editor/Module.cs

@@ -17,6 +17,8 @@ public static void Initialize()
             AssetsPlugin.RegisterPlugin(typeof(CoreAssetsEditorPlugin));
             // Initialize translation
             TranslationManager.Instance.RegisterProvider(new GettextTranslationProvider());
+            // HACK
+            Presentation.Quantum.ViewModels.NodeViewModel.UnsetValue = System.Windows.DependencyProperty.UnsetValue;
         }
     }
 }

sources/presentation/Stride.Core.Presentation.Quantum/ViewModels/NodeViewModel.cs

@@ -47,6 +47,8 @@ internal class DifferentValuesObject { public readonly string Name = "DifferentV
 
         public static readonly object DifferentValues = new DifferentValuesObject();
 
+        public static object UnsetValue;
+
         static NodeViewModel()
         {
             typeof(NodeViewModel).GetProperties().Select(x => x.Name).ForEach(x => ReservedNames.Add(x));
@@ -317,7 +319,7 @@ public object GetAssociatedData(string name)
         public object GetDynamicObject(string name)
         {
             name = EscapeName(name);
-            return GetChild(name) ?? GetCommand(name) ?? GetAssociatedData(name);
+            return GetChild(name) ?? GetCommand(name) ?? GetAssociatedData(name) ?? UnsetValue;
         }
 
         /// <inheritdoc/>