public function transform($value)
    {
        if ( $value ) {
            $from = '';
            if ( $value->getFrom() ) {
                $from = $value->getFrom()->format('Y-m-d');
            }
            $to = '';
            if ( $value->getTo() ) {
                $to = $value->getTo()->format('Y-m-d');
            }
            return sprintf(
                '%s%s%s',
                $from,
                $this->dateSeparator,
                $to
            );
        }
    }