private void addListModelsNull() {
    personListModel = new DefaultListModel();
    groupListModel = new DefaultListModel();
    roomListModel = new DefaultListModel();

    personsList.setModel(personListModel);
    groupList.setModel(groupListModel);
    roomList.setModel(roomListModel);

    ArrayList<Room> rooms = main.getRooms();
    //		fyll inn romlisten med rom
    for (int i = 0; i < rooms.size(); i++) {
      roomListModel.addElement(rooms.get(i));
    }
  }
  private void addListModelsNotNull() {
    personListModel = new DefaultListModel();
    groupListModel = new DefaultListModel();
    roomListModel = new DefaultListModel();

    personsList.setModel(personListModel);
    groupList.setModel(groupListModel);
    roomList.setModel(roomListModel);

    //		fyll inn personlisten med participants
    for (int i = 0; i < model.getParticipantLength(); i++) {
      personListModel.addElement(model.getParticipant(i).getUser());
    }

    ArrayList<Room> rooms = main.getRooms();
    //		fyll inn romlisten med rom
    for (int i = 0; i < rooms.size(); i++) {
      roomListModel.addElement(rooms.get(i));
    }

    roomList.setSelectedValue(model.getRoom(), true);
  }