add comment about when component is null

also remove this fix from the release notes

Author: vkovec

Assets/FbxExporters/Editor/FbxPrefabAutoUpdater.cs

@@ -989,7 +989,12 @@ public HashSet<GameObject> ImplementUpdates(FbxPrefab prefabInstance)
                                 prefabComponent = prefabXfo.gameObject.AddComponent(fbxComponent.t);
                                 Log("created component {0}:{1}", nodeName, fbxComponent.t);
                             }
-                            // check that the component exists before copying to it
+                            // Check that the component exists before copying to it.
+                            // This happens for Rect Transform components as the fbx
+                            // contains a Transform which it tries to add/update on the
+                            // prefab, but fails because you cannot have both a Transform
+                            // and a Rect Transform
+                            // UNI-29179 TODO: better handling of Rect Transforms
                             if (!prefabComponent) {
                                 continue;
                             }

RELEASE_NOTES.md

@@ -17,7 +17,6 @@ FIXES
 * Maya Unity Integration: lock export set so it doesn't accidentally get deleted
 * Convert to Prefab: Fix so convert to prefab doesn't lose Object references in scripts
 * Export Settings: Fix so MayaLT cannot be selected using "Browse" on Mac
-* Fbx Prefab: Fix update fails if trying to update component that doesn't exist
 
 **Version**: 1.0.0b1