Check if either array is null before diffing

Reviewed By: sebmarkbage

Differential Revision: D3219392

fb-gh-sync-id: fd6ef2e2c2d7b661a06c857b25b007701340e20a
fbshipit-source-id: fd6ef2e2c2d7b661a06c857b25b007701340e20a

Libraries/ART/ReactNativeART.js

@@ -23,7 +23,7 @@ var merge = require('merge');
 // Diff Helpers
 
 function arrayDiffer(a, b) {
-  if (a == null) {
+  if (a == null || b == null) {
     return true;
   }
   if (a.length !== b.length) {