dont try to look at the keys of zero-length arrays or arguments objects when calling each()

underscore.js

@@ -42,7 +42,7 @@
     try {
       if (obj.forEach) {
         obj.forEach(iterator, context);
-      } else if (obj.length) {
+      } else if (obj.length || obj.length === 0) {
         for (var i=0, l=obj.length; i<l; i++) iterator.call(context, obj[i], i, obj);
       } else {
         var keys = _.keys(obj), l = keys.length;