walk: filter null objects

Author: juliangruber

lib/walk.js

@@ -2,7 +2,7 @@
 module.exports = function walk(objects, key){
   var value;
   for (var i = objects.length - 1; i >= 0; i--) {
-    if (objects[i][key]) value = objects[i][key];
+    if (objects[i] && objects[i][key]) value = objects[i][key];
   }
   return value;
 };