public function filterByClosed($closed = null, $comparison = null)
    {
        if (is_string($closed)) {
            $closed = in_array(strtolower($closed), array('false', 'off', '-', 'no', 'n', '0', '')) ? false : true;
        }

        return $this->addUsingAlias(DealerShedulesVersionTableMap::CLOSED, $closed, $comparison);
    }