code: public List<Jid> getOccupiedRooms(DomainBareJid mucLightService)
              throws NoResponseException, XMPPErrorException, NotConnectedException, InterruptedException {
          DiscoverItems result = ServiceDiscoveryManager.getInstanceFor(connection()).discoverItems(mucLightService);
          List<DiscoverItems.Item> items = result.getItems();
          List<Jid> answer = new ArrayList<>(items.size());
  
          for (DiscoverItems.Item item : items) {
              Jid mucLight = item.getEntityID();
              answer.add(mucLight);
          }
  
          return answer;
      }
docs: Returns a List of the rooms the user occupies.
  
  @param mucLightService
  @return a List of the rooms the user occupies.
  @throws XMPPErrorException
  @throws NoResponseException
  @throws NotConnectedException
  @throws InterruptedException