Load/dump individual message fields
        :param msg:
        :param fields:
        :param obj:
        :return:

async def message_fields(self, msg, fields, obj=None):
        """
        Load/dump individual message fields
        :param msg:
        :param fields:
        :param obj:
        :return:
        """
        for field in fields:
            await self.message_field(msg, field, obj)
        return msg