code: async def load_message(self, msg_type, msg=None):
          
          msg = msg_type() if msg is None else msg
          fields = msg_type.f_specs() if msg_type else msg.__class__.f_specs()
          for field in fields:
              await self.message_field(msg, field)
  
          return msg
docs: Loads message if the given type from the reader.
          Supports reading directly to existing message.
  
          :param msg_type:
          :param msg:
          :return: