/**
  * Overridden to use _idFieldName by default.
  *
  * @param null $valueField
  * @param string $labelField
  * @param array $additional
  * @return array
  */
 protected function _toOptionArray($valueField = null, $labelField = 'name', $additional = [])
 {
     if ($valueField === null) {
         $valueField = $this->getIdFieldName();
     }
     return parent::_toOptionArray($valueField, $labelField, $additional);
 }