protected function _bulk(Query $query = null)
    {
        $field = $this->getConfig('field');
        $expression = [new QueryExpression(sprintf('%1$s= NOT %1$s', $field))];
        $query->update()->set($expression);
        $statement = $query->execute();
        $statement->closeCursor();

        return (bool)$statement->rowCount();
    }