validate from-to
        :param start: Start Day(YYYYMMDD)
        :param end: End Day(YYYYMMDD)
        :return: None or MlbAmException

def _validate_datetime_from_to(cls, start, end):
        """
        validate from-to
        :param start: Start Day(YYYYMMDD)
        :param end: End Day(YYYYMMDD)
        :return: None or MlbAmException
        """
        if not start <= end:
            raise MlbAmBadParameter("not Start Day({start}) <= End Day({end})".format(start=start, end=end))