code: function serialize(obj) {
      if (!isObject(obj)) return obj;
      var pairs = [];
      for (var key in obj) {
          if (null != obj[key]) {
              pairs.push(encodeURIComponent(key)
                  + '=' + encodeURIComponent(obj[key]));
          }
      }
      return pairs.join('&');
  }
docs: Serialize the given `obj`.
  
  @param {Object} obj
  @return {String}
  @api private