#vulnerable code 
                                @Override
    public T set(int index, T element) {
        T previousElement = this.get(index);
        internalIndexedAdd(index, element, true);
        return previousElement;
    } 
                            #location 4 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                @Override
    public T set(int index, T element) {
        T previousElement = this.get(index);
        internalIndexedAdd(index, element);
        return previousElement;
    }