protected ForwardingConcurrentMap() {}

  @Override
  protected abstract ConcurrentMap<K, V> delegate();

  @CanIgnoreReturnValue
  @Override
  @CheckForNull
  public V putIfAbsent(K key, V value) {
    return delegate().putIfAbsent(key, value);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean remove(@CheckForNull Object key, @CheckForNull Object value) {
    return delegate().remove(key, value);
  }

  protected ForwardingConcurrentMap() {}

  @Override
  protected abstract ConcurrentMap<K, V> delegate();

  @CanIgnoreReturnValue
  @Override
  @CheckForNull
  public V putIfAbsent(K key, V value) {
    return delegate().putIfAbsent(key, value);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean remove(@CheckForNull Object key, @CheckForNull Object value) {
    return delegate().remove(key, value);
  }