assertTrue(Thread.holdsLock(mutex));
      return delegate().pollFirstEntry();
    }

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

    @Override
    public NavigableMap<K, V> subMap(
        K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {

  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)

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

  @Override
  public abstract ImmutableSortedMultiset<E> headMultiset(E upperBound, BoundType boundType);

  @Override