public static function toList($string, string $separator = self::SEPARATOR_LIST)
    {
        if (null === $string) {
            return null;
        }

        $withoutParenthesis = self::removeParenthesis($string);
        if ('' === $withoutParenthesis) {
            return [];
        }


        if (strstr($withoutParenthesis, $separator) !== false) {
            return explode($separator, $withoutParenthesis);
        }

        return [$withoutParenthesis];
    }