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