code: function() {
          if (!this.isCurrent()) {
            return;
          }
          var authData = this.get('authData');
          if (!authData) {
            return;
          }
          AV._objectEach(this.get('authData'), function(value, key) {
            if (!authData[key]) {
              delete authData[key];
            }
          });
        }
docs: Removes null values from authData (which exist temporarily for
  unlinking)
  @private