cann't overide method 'exec' in extended Phalcon\Db\Adapter\Pdo\Postgres

I try to overide method like in https://github.com/phalcon/incubator/blob/master/Library/Phalcon/Db/Adapter/Cacheable/Mysql.php

class Postgresql extends \Phalcon\Db\Adapter\Pdo\Postgresql
{
 public function query($sqlStatement, $bindParams = null, $bindTypes = null)
    {
      ...
     $data = parent::query($sqlStatement, $bindParams, $bindTypes);//RuntimeException
     }
}

but have error - RuntimeException: Trying to call method query on a non-object
by documentetion this method is public https://docs.phalcon.io/ru/latest/api/Phalcon_Db_Adapter_Pdo_Postgresql.html reflaction on method also say that is public. What wrong? phalcon 2.0.8