Added check for data provider to fix #330

XRTK-Core/Packages/com.xrtk.core/Services/MixedRealityToolkit.cs

@@ -373,6 +373,13 @@ private void InitializeServiceLocator()
                         {
                             foreach (var controllerDataProvider in ActiveProfile.InputSystemProfile.ControllerDataProvidersProfile.RegisteredControllerDataProviders)
                             {
+                                //If the DataProvider cannot be resolved, this is likely just a configuration / package missmatch.  User simply needs to be warned, not errored.
+                                if (controllerDataProvider.DataProviderType.Type == null)
+                                {
+                                    Debug.LogWarning($"Could not load the configured provider ({controllerDataProvider.DataProviderName})\n\nThis is most likely because the XRTK UPM package for that provider is currently not registered\nCheck the installed packages in the Unity Package Manager\n\n");
+                                    continue;
+                                }
+
                                 if (!CreateAndRegisterService<IMixedRealityControllerDataProvider>(
                                     controllerDataProvider.DataProviderType,
                                     controllerDataProvider.RuntimePlatform,