#vulnerable code 
                                @Override
    public V put(K key, V value) {
        V previousValue = get(key);
        internalPut(key, value, true);
        return previousValue;
    } 
                            #location 4 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                @Override
    public V put(K key, V value) {
        V previousValue = get(key);
        internalPut(key, value);
        return previousValue;
    }