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());
    }
  }
 /**
  * Rejects the given invitation with the specified reason.
  *
  * @param whiteboardOpSet the operation set to use for rejecting the invitation
  * @param invitation the invitation to reject
  * @param reason the reason for the rejection
  */
 public void rejectInvitation(
     OperationSetWhiteboarding whiteboardOpSet, WhiteboardInvitation invitation, String reason) {
   whiteboardOpSet.rejectInvitation(invitation, reason);
 }