assertEquals(c, navigableMap.pollLastEntry());
    assertEquals(entries.subList(0, entries.size() - 1), copyToList(navigableMap.entrySet()));
  }

  @MapFeature.Require(absent = SUPPORTS_REMOVE)
  @CollectionSize.Require(SEVERAL)
  public void testPollLastUnsupported() {
    assertThrows(UnsupportedOperationException.class, () -> navigableMap.pollLastEntry());
  }

  @CollectionSize.Require(SEVERAL)

  public void testPollLast() {
    assertEquals(c, sortedMultiset.pollLastEntry());
    assertEquals(asList(a, b), copyToList(sortedMultiset.entrySet()));
  }

  @CollectionFeature.Require(absent = SUPPORTS_REMOVE)
  @CollectionSize.Require(SEVERAL)
  public void testPollLastUnsupported() {
    assertThrows(UnsupportedOperationException.class, () -> sortedMultiset.pollLastEntry());
  }

  @CollectionSize.Require(SEVERAL)

  public void testPollLast() {
    assertEquals(c, sortedMultiset.pollLastEntry());
    assertEquals(asList(a, b), copyToList(sortedMultiset.entrySet()));
  }

  @CollectionFeature.Require(absent = SUPPORTS_REMOVE)
  @CollectionSize.Require(SEVERAL)
  public void testPollLastUnsupported() {
    assertThrows(UnsupportedOperationException.class, () -> sortedMultiset.pollLastEntry());
  }

  @CollectionSize.Require(SEVERAL)

  }

  @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 nullableSynchronizedEntry(delegate().pollFirstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> pollLastEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().pollLastEntry(), mutex);
      }
    }

    @Override
    public NavigableMap<K, V> subMap(

        return nullableSynchronizedEntry(delegate().pollFirstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> pollLastEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().pollLastEntry(), mutex);
      }
    }

    @Override
    public NavigableMap<K, V> subMap(

   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  @CheckForNull
  public final Entry<K, V> pollLastEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  public ImmutableSortedMap<K, V> descendingMap() {
    // TODO(kevinb): The descendingMap is never actually cached at all. Either:

   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  @CheckForNull
  public final Entry<K, V> pollLastEntry() {
    throw new UnsupportedOperationException();
  }

  @Override
  public ImmutableSortedMap<K, V> descendingMap() {
    // TODO(kevinb): The descendingMap is never actually cached at all. Either: