def remove_parenthesis_around_tz(cls, timestr):
        """get rid of parenthesis around timezone: (GMT) => GMT

        :return: the new string if parenthesis were found, `None` otherwise
        """
        parenthesis = cls.TIMEZONE_PARENTHESIS.match(timestr)
        if parenthesis is not None:
            return parenthesis.group(1)
get rid of parenthesis around timezone: (GMT) => GMT

        :return: the new string if parenthesis were found, `None` otherwise