fix(Runtime): FaceTrackingSystem Correctives now optional

Summary: The correctives field of `FaceTrackingSystem.cs` should be optional because not everyone will have a correctives file on-hand.

Reviewed By: andkim-meta

Differential Revision: D42488038

fbshipit-source-id: 2095b151acee61cac1f437c7218c15b0db767508

Runtime/Scripts/Tooltips.cs

@@ -535,7 +535,7 @@ public static class FaceTrackingSystemTooltips
             "OVR face expressions component.";
 
         public const string CorrectiveShapesDriver =
-            "Corrective shapes driver component.";
+            "Optional corrective shapes driver component.";
 
         public const string BlendshapeModifier =
             "Optional blendshape modifier component.";

Runtime/Scripts/Tracking/FaceTrackingData/FaceTrackingSystem.cs

@@ -28,9 +28,10 @@ public class FaceTrackingSystem : MonoBehaviour
         protected OVRFaceExpressions _ovrFaceExpressions;
 
         /// <summary>
-        /// Corrective shapes driver component.
+        /// Optional corrective shapes driver component.
         /// </summary>
         [SerializeField]
+        [Optional]
         [Tooltip(FaceTrackingSystemTooltips.CorrectiveShapesDriver)]
         protected CorrectiveShapesDriver _correctiveShapesDriver;
 
@@ -43,7 +44,7 @@ public class FaceTrackingSystem : MonoBehaviour
         protected BlendshapeModifier _blendshapeModifier;
 
         /// <summary>
-        /// If true, the corrective driver will run and apply correctives.
+        /// If true, the correctives driver will apply correctives.
         /// </summary>
         public bool CorrectivesEnabled { get; set; }
 
@@ -61,7 +62,6 @@ private void Awake()
         {
             Assert.IsNotNull(_blendShapeMapping);
             Assert.IsNotNull(_ovrFaceExpressions);
-            Assert.IsNotNull(_correctiveShapesDriver);
             ExpressionWeights = new float[(int)OVRFaceExpressions.FaceExpression.Max];
 
             CorrectivesEnabled = true;
@@ -82,7 +82,7 @@ private void Update()
                 UpdateAllMeshesUsingFaceTracking();
             }
 
-            if (CorrectivesEnabled)
+            if (CorrectivesEnabled && _correctiveShapesDriver != null)
             {
                 _correctiveShapesDriver.ApplyCorrectives();
             }