Fix reduceRight() so that if you don't pass in an initial value, the last item in the collection is used

underscore.js

@@ -107,7 +107,9 @@
   _.reduceRight = _.foldr = function(obj, iterator, memo, context) {
     if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {
       if (context) iterator = _.bind(iterator, context);
-      return obj.reduceRight(iterator, memo);
+      var args = [iterator];
+      if (memo !== undefined) args.push(memo);
+      return obj.reduceRight.apply(obj, args);
     }
     var reversed = (_.isArray(obj) ? obj.slice() : _.toArray(obj)).reverse();
     return _.reduce(reversed, iterator, memo, context);