protected function map($dataRow)
    {
        $data = $this->getData($dataRow);
        $pmk = $this->getParentPrimaryKey();
        $entity = (isset($data[$pmk]) && $data[$pmk])
            ? $this->getParentEntityMapper()->createFrom($data)
            : null;
        return null == $entity ? null : $this->registerEntity($entity);
    }