code: public void unsubscribeFailed(int arg0,
  			SubscriptionClientChildSbbLocalObject subscriptionChild) {
  		try {
  			final String notifier = subscriptionChild.getSubscriptionData().getNotifierURI();
  			subscriptionChild.remove();
  			getParent().unsubscribeFailed(
  					arg0,
  					(XDMClientChildSbbLocalObject) this.sbbContext
  							.getSbbLocalObject(), notifier);
  		} catch (Exception e) {
  			tracer.severe("Unexpected exception on callback!", e);
  		}
  	}
docs: two easy cases.