code: function (target, source) {
          var key;
  
          for (key in source) {
              if (source.hasOwnProperty(key) && !_.isUndefined(source[key])) {
                  target[key] = source[key];
              }
          }
  
          return target;
      }
docs: Merges defined keys from the target object onto the source object.
  
  @param {Object} target
  @param {Object} source
  @returns {Object}