cleanup: remove redundant isArray check from each series

Author: shakyShane

lib/utils.js

@@ -263,9 +263,6 @@ var utils = {
     },
     eachSeries: function (arr, iterator, callback) {
         callback = callback || function () {};
-        if (!Array.isArray(arr) || !arr.length) {
-            return callback();
-        }
         var completed = 0;
         var iterate = function () {
             iterator(arr[completed], function (err) {