}

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

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

  @Override
  public @Nullable V put(K key, V value) {
    return delegate.put(checkValid(key), value);
  }

  @Override

  }

  @Override
  @CheckForNull
  public Entry<K, V> pollFirstEntry() {
    return Iterators.pollNext(entryIterator());
  }

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

  @Override
  @ParametricNullness
  public K firstKey() {
    Entry<K, V> entry = firstEntry();
    if (entry == null) {

  }

  @Override
  @CheckForNull
  public Entry<E> pollFirstEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  @CheckForNull
  public Entry<E> pollLastEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  public SortedMultiset<E> headMultiset(E upperBound, BoundType boundType) {

    public E pollFirst() {
      return getElementOrNull(multiset().pollFirstEntry());
    }

    @Override
    @CheckForNull
    public E pollLast() {
      return getElementOrNull(multiset().pollLastEntry());
    }

    @Override
    public NavigableSet<E> subSet(
        @ParametricNullness E fromElement,
        boolean fromInclusive,
        @ParametricNullness E toElement,

  }

  @Override
  @CheckForNull
  public Entry<E> pollFirstEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  @CheckForNull
  public Entry<E> pollLastEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  public SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType) {

      return standardLastEntry();
    }

    @Override
    public Entry<E> pollFirstEntry() {
      return standardPollFirstEntry();
    }

    @Override
    public Entry<E> pollLastEntry() {
      return standardPollLastEntry();
    }

    @Override
    public SortedMultiset<E> subMultiset(
        E lowerBound, BoundType lowerBoundType, E upperBound, BoundType upperBoundType) {

  }

  @Override
  @CheckForNull
  public Entry<K, V> pollFirstEntry() {
    return Iterators.pollNext(entryIterator());
  }

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

  @Override
  @ParametricNullness
  public K firstKey() {
    Entry<K, V> entry = firstEntry();
    if (entry == null) {

      return standardLastEntry();
    }

    @Override
    public Entry<E> pollFirstEntry() {
      return standardPollFirstEntry();
    }

    @Override
    public Entry<E> pollLastEntry() {
      return standardPollLastEntry();
    }

    @Override
    public SortedMultiset<E> subMultiset(
        E lowerBound, BoundType lowerBoundType, E upperBound, BoundType upperBoundType) {

     */

    @Override
    public @Nullable Entry<K, V> pollFirstEntry() {
      return standardPollFirstEntry();
    }

    @Override
    public @Nullable Entry<K, V> pollLastEntry() {
      return standardPollLastEntry();
    }

    @Override
    public NavigableMap<K, V> descendingMap() {
      return new StandardDescendingMap();
    }

    @Override

    public Entry<K, V2> pollFirstEntry() {
      return transformEntry(fromMap().pollFirstEntry());
    }

    @Override
    @CheckForNull
    public Entry<K, V2> pollLastEntry() {
      return transformEntry(fromMap().pollLastEntry());
    }

    @Override
    public NavigableMap<K, V2> subMap(
        @ParametricNullness K fromKey,
        boolean fromInclusive,