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

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

  @Override

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

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