validate datetime value
        :param value: datetime value
        :return: None or validators.Invalid or MlbAmException

def _validate_datetime(cls, value):
        """
        validate datetime value
        :param value: datetime value
        :return: None or validators.Invalid or MlbAmException
        """
        datetime_check = validators.Int()
        datetime_check.to_python(value)
        if len(value) != 8:
            raise MlbAmBadParameter("Length Error:{value}({length})".format(value=value, length=len(value)))