protected function makeIndexDDL($type, $name = null)
    {
        return implode(
            ' ',
            array_filter(
                [
                    strtoupper($type),
                    $name !== null ? '`' . $name . '`' : null,
                    $this->makeIndexedColumnsDDL(),
                    $this->hasComment() ? "COMMENT '" . addslashes($this->getComment()) . "'" : null
                ]
            )
        );
    }