#vulnerable code 
                                @Override
    public boolean tryAdvance(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        if (!exhausted) {
            ReentrantLock lock = queueLock;
            Object p = current;
            E e = null;
            lock.lock();
            try {
                if (p != null || (p = getQueueFirst(queue)) != null)
                    do {
                        e = getNodeItem(p);
                        p = succ(p);
                    } while (e == null && p != null);
            } finally {
                // checkInvariants();
                lock.unlock();
            }
            exhausted = ((current = p) == null);
            if (e != null) {
                action.accept(e);
                return true;
            }
        }
        return false;
    } 
                            #location 19 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                @Override
    public boolean tryAdvance(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        if (!exhausted) {
            E e = null;
            ReentrantLock lock = queueLock;
            lock.lock();
            try {
                Object p;
                if ((p = current) != null || (p = getQueueFirst(queue)) != null)
                    do {
                        e = getNodeItem(p);
                        p = succ(p);
                    } while (e == null && p != null);
                exhausted = ((current = p) == null);
            } finally {
                // checkInvariants();
                lock.unlock();
            }
            if (e != null) {
                action.accept(e);
                return true;
            }
        }
        return false;
    }