Fix Case Where Node Is Deallocated While Visible (#2171)

* Attempt to reproduce supplementary crash

* Get closer with supplementary issue testing

* Alright! We have a repro!

* The investigation continues

* Fixed!

AsyncDisplayKit/ASDisplayNode.mm

@@ -1468,7 +1468,7 @@ static inline CATransform3D _calculateTransformFromReferenceToTarget(ASDisplayNo
   }
 
   ASDisplayNodeAssert(_flags.layerBacked, @"We shouldn't get called back here if there is no layer");
-  return (id<CAAction>)[NSNull null];
+  return (id)kCFNull;
 }
 
 #pragma mark - Managing the Node Hierarchy