#vulnerable code 
                                @Override
    public boolean addAll(Collection<? extends T> collection) {
        boolean success = true;
        for (T element : collection) {
            success &= internalAdd(element, false);
        }
        refreshStorage(true);
        return success;
    } 
                            #location 5 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                @Override
    public boolean addAll(Collection<? extends T> collection) {
        boolean success = true;
        for (T element : collection) {
            success &= internalAdd(element);
        }
        return success;
    }