Send the latest non-null theme directly to the new action

Author: keveleigh

org.mixedrealitytoolkit.theming/Theming/ThemeDataSource.cs

@@ -53,13 +53,16 @@ public void SetValueWithoutNotify(Theme newValue)
 
         public void AddListener(UnityAction<ChangeEvent<Theme>> action)
         {
+            if (action == null) { return; }
             onThemeChanged.AddListener(action);
+            if (activeTheme == null) { return; }
             using ChangeEvent<Theme> changeEvent = ChangeEvent<Theme>.GetPooled(null, activeTheme);
-            SendEvent(changeEvent);
+            action.Invoke(changeEvent);
         }
 
         public void RemoveListener(UnityAction<ChangeEvent<Theme>> action)
         {
+            if (action == null) { return; }
             onThemeChanged.RemoveListener(action);
         }