code: public void join(Resourcepart nickname) throws NoResponseException, XMPPErrorException,
                      NotConnectedException, InterruptedException, NotAMucServiceException {
          MucEnterConfiguration.Builder builder = getEnterConfigurationBuilder(nickname);
          join(builder.build());
      }
docs: Joins the chat room using the specified nickname. If already joined
  using another nickname, this method will first leave the room and then
  re-join using the new nickname. The default connection timeout for a reply
  from the group chat server that the join succeeded will be used. After
  joining the room, the room will decide the amount of history to send.
  
  @param nickname the nickname to use.
  @throws NoResponseException
  @throws XMPPErrorException if an error occurs joining the room. In particular, a
  401 error can occur if no password was provided and one is required; or a
  403 error can occur if the user is banned; or a
  404 error can occur if the room does not exist or is locked; or a
  407 error can occur if user is not on the member list; or a
  409 error can occur if someone is already in the group chat with the same nickname.
  @throws NoResponseException if there was no response from the server.
  @throws NotConnectedException
  @throws InterruptedException
  @throws NotAMucServiceException