public function delete_group_option(string $id_option, string $id_group): ?int
  {
    if ( $id_option = $this->_get_id_option($id_option) ){
      return $this->db->delete($this->class_cfg['table'], [
        $this->fields['id_option'] => $id_option,
        $this->fields['id_group'] => $id_group
      ]);
    }
    return null;
  }