#fixed code
                                @Override
    public void start() {
        Log.debug("Start");
        notificationController = new NotificationController();

        EventBusService eventBusService = NulsContext.getServiceBean(EventBusService.class);
        eventBusService.subscribeEvent(BaseEvent.class,notificationController.getNulsEventHandler());

        notificationController.setListenPort(port);
        notificationController.start();
    }
#vulnerable code 
                                @Override
    public void start() {
        Log.debug("Start");
        notificationController = new NotificationController();

        EventBusService eventBusService = NulsContext.getServiceBean(EventBusService.class);
        eventBusService.subscribeEvent(BaseEvent.class,notificationController.getNulsEventHandler());

        notificationController.setListenPort(port);
        notificationController.start();


        NulsEventHandler handler = new NulsEventHandler();

        String subscribeId = NulsContext.getServiceBean(EventBusService.class).subscribeEvent(BaseEvent.class,handler);
        Log.debug("subscribe base event:"+subscribeId);
    } 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE