Fatal system crash due to NullPointerException

    private void notifyEventListenerLocked(Service service, int eventType) {

        IEventListener listener = service.mServiceInterface;

        AccessibilityEvent event = service.mPendingEvents.get(eventType);

        // Check for null here because there is a concurrent scenario in which this

        // happens: 1) A binder thread calls notifyAccessibilityServiceDelayedLocked

        // which posts a message for dispatching an event. 2) The message is pulled

        // from the queue by the handler on the service thread and the latter is

        // just about to acquire the lock and call this method. 3) Now another binder

        // thread acquires the lock calling notifyAccessibilityServiceDelayedLocked

        // so the service thread waits for the lock; 4) The binder thread replaces

        // the event with a more recent one (assume the same event type) and posts a

        // dispatch request releasing the lock. 5) Now the main thread is unblocked and

        // dispatches the event which is removed from the pending ones. 6) And ... now

        // the service thread handles the last message posted by the last binder call

        // but the event is already dispatched and hence looking it up in the pending

        // ones yields null. This check is much simpler that keeping count for each

        // event type of each service to catch such a scenario since only one message

        // is processed at a time.

        if (event == null) {

            return;

        }

        service.mPendingEvents.remove(eventType);

        try {

            if (mSecurityPolicy.canRetrieveWindowContent(service)) {