delegate().clear();
      }
    };
  }

  @Override
  public @Nullable Entry<K, V> firstEntry() {
    return delegate.firstEntry();
  }

  @Override
  public K firstKey() {
    return delegate.firstKey();
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(K key) {
    return delegate.floorEntry(checkValid(key));
  }

  @Override
  public @Nullable K floorKey(K key) {

    return Iterables.<@Nullable Entry<K, V>>getFirst(entrySet(), null);
  }

  /**
   * A sensible definition of {@link #firstKey} in terms of {@code firstEntry}. If you override
   * {@code firstEntry}, you may wish to override {@code firstKey} to forward to this
   * implementation.
   */
  protected K standardFirstKey() {
    Entry<K, V> entry = firstEntry();
    if (entry == null) {

    return Iterables.<@Nullable Entry<K, V>>getFirst(entrySet(), null);
  }

  /**
   * A sensible definition of {@link #firstKey} in terms of {@code firstEntry}. If you override
   * {@code firstEntry}, you may wish to override {@code firstKey} to forward to this
   * implementation.
   */
  protected K standardFirstKey() {
    Entry<K, V> entry = firstEntry();
    if (entry == null) {

        // Server indicates required -> required+enabled
        Smb2NegotiateResponse firstReq = mock(Smb2NegotiateResponse.class);
        when(firstReq.isSigningRequired()).thenReturn(true);
        assertEquals(Smb2Constants.SMB2_NEGOTIATE_SIGNING_REQUIRED | Smb2Constants.SMB2_NEGOTIATE_SIGNING_ENABLED,
                transport.getRequestSecurityMode(firstReq));
    }

    @Test

    @Override
    public @Nullable Comparator<? super K> comparator() {
      return sortedMap().comparator();
    }

    @Override
    @ParametricNullness
    public K firstKey() {
      return sortedMap().firstKey();
    }

    @Override
    @ParametricNullness
    public K lastKey() {
      return sortedMap().lastKey();
    }

    @Override

  }

  @Override
  public @Nullable Entry<K, V> pollLastEntry() {
    return Iterators.pollNext(descendingEntryIterator());
  }

  @Override
  @ParametricNullness
  public K firstKey() {
    Entry<K, V> entry = firstEntry();
    if (entry == null) {
      throw new NoSuchElementException();
    } else {
      return entry.getKey();
    }
  }

  @Override
  @ParametricNullness

    @Override
    public @Nullable Comparator<? super K> comparator() {
      return fromMap().comparator();
    }

    @Override
    @ParametricNullness
    public K firstKey() {
      return fromMap().firstKey();
    }

    @Override
    public SortedMap<K, V2> headMap(@ParametricNullness K toKey) {
      return transformEntries(fromMap().headMap(toKey), transformer);
    }

    @Override
    public @Nullable Comparator<? super K> comparator() {
      return fromMap().comparator();
    }

    @Override
    @ParametricNullness
    public K firstKey() {
      return fromMap().firstKey();
    }

    @Override
    public SortedMap<K, V2> headMap(@ParametricNullness K toKey) {
      return transformEntries(fromMap().headMap(toKey), transformer);
    }

      return new StandardNavigableKeySet();
    }

    @Override
    public NavigableSet<K> descendingKeySet() {
      return standardDescendingKeySet();
    }

    @Override
    public K firstKey() {
      return standardFirstKey();
    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      return standardHeadMap(toKey);
    }

    @Override
    public K lastKey() {

  }

  @Override
  public Comparator<? super K> comparator() {
    return comparator;
  }

  @Override
  public @Nullable K firstKey() {
    return sortedDelegate.firstKey();
  }

  @Override
  public @Nullable K lastKey() {
    return sortedDelegate.lastKey();
  }

  @Nullable K higher(K k) {