code: async def get(self, uid: int, cached_msg: CachedMessage = None,
                    requirement: FetchRequirement = FetchRequirement.METADATA) \
              -> Optional[MessageT]:
          
          ...
docs: Return the message with the given UID.
  
          Args:
              uid: The message UID.
              cached_msg: The last known cached message.
              requirement: The data required from each message.
  
          Raises:
              IndexError: The UID is not valid in the mailbox.