public WhiteboardSessionManager() {
    if (WhiteboardActivator.getWhiteboardOperationSets() == null) return;

    Iterator opSets = WhiteboardActivator.getWhiteboardOperationSets().iterator();

    while (opSets.hasNext()) {
      OperationSetWhiteboarding whiteboardOpSet = (OperationSetWhiteboarding) opSets.next();

      whiteboardOpSet.addInvitationListener(new InvitationListener());
      whiteboardOpSet.addPresenceListener(new PresenceListener());
    }
  }