code: public static synchronized MultiUserChatManager getInstanceFor(XMPPConnection connection) {
          MultiUserChatManager multiUserChatManager = INSTANCES.get(connection);
          if (multiUserChatManager == null) {
              multiUserChatManager = new MultiUserChatManager(connection);
              INSTANCES.put(connection, multiUserChatManager);
          }
          return multiUserChatManager;
      }
docs: Get a instance of a multi user chat manager for the given connection.
  
  @param connection
  @return a multi user chat manager.