Merge pull request #2072 from davidkline-ms/nullRef2053

handle case of no MotionControllerVisualizer singleton

Assets/HoloToolkit/Common/Scripts/Singleton.cs

@@ -62,6 +62,16 @@ public static bool IsInitialized
             }
         }
 
+        /// <summary>
+        /// Awake and OnEnable safe way to check if a Singleton is initialized.
+        /// </summary>
+        /// <returns>The value of the Singleton's IsInitialized property</returns>
+        public static bool ConfirmInitialized()
+        {
+            T access = Instance;
+            return IsInitialized;
+        }
+
         /// <summary>
         /// Base Awake method that sets the Singleton's unique instance.
         /// Called by Unity when initializing a MonoBehaviour.

Assets/HoloToolkit/Input/Scripts/Utilities/ControllerFinder.cs

@@ -42,6 +42,12 @@ public InteractionSourceHandedness Handedness
         protected virtual void OnEnable()
         {
 #if UNITY_WSA && UNITY_2017_2_OR_NEWER
+            if (!MotionControllerVisualizer.ConfirmInitialized())
+            {
+                // The motion controller visualizer singleton could not be found.
+                return;
+            }
+
             // Look if the controller has loaded.
             if (MotionControllerVisualizer.Instance.TryGetControllerModel(handedness, out ControllerInfo))
             {