result = Multisets.immutableEntry(result.getElement(), result.getCount());
      entryIterator.remove();
      return result;
    }
    return null;
  }

  @Override
  public SortedMultiset<E> subMultiset(
      @ParametricNullness E fromElement,
      BoundType fromBoundType,
      @ParametricNullness E toElement,
      BoundType toBoundType) {

      result = Multisets.immutableEntry(result.getElement(), result.getCount());
      entryIterator.remove();
      return result;
    }
    return null;
  }

  @Override
  public SortedMultiset<E> subMultiset(
      @ParametricNullness E fromElement,
      BoundType fromBoundType,
      @ParametricNullness E toElement,
      BoundType toBoundType) {

      return standardPollFirstEntry();
    }

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

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

    @Override

   * elements outside its range.
   *
   * <p>This method is equivalent to {@code tailMultiset(lowerBound,
   * lowerBoundType).headMultiset(upperBound, upperBoundType)}.
   */
  SortedMultiset<E> subMultiset(
      @ParametricNullness E lowerBound,
      BoundType lowerBoundType,
      @ParametricNullness E upperBound,
      BoundType upperBoundType);

  /**

   * elements outside its range.
   *
   * <p>This method is equivalent to {@code tailMultiset(lowerBound,
   * lowerBoundType).headMultiset(upperBound, upperBoundType)}.
   */
  SortedMultiset<E> subMultiset(
      @ParametricNullness E lowerBound,
      BoundType lowerBoundType,
      @ParametricNullness E upperBound,
      BoundType upperBoundType);

  /**

  }

  /**
   * Returns {@code true} if {@code subMultiset.count(o) <= superMultiset.count(o)} for all {@code
   * o}.
   *
   * @since 10.0
   */
  @CanIgnoreReturnValue
  public static boolean containsOccurrences(Multiset<?> superMultiset, Multiset<?> subMultiset) {
    checkNotNull(superMultiset);
    checkNotNull(subMultiset);
    for (Entry<?> entry : subMultiset.entrySet()) {

  }

  /**
   * Returns {@code true} if {@code subMultiset.count(o) <= superMultiset.count(o)} for all {@code
   * o}.
   *
   * @since 10.0
   */
  @CanIgnoreReturnValue
  public static boolean containsOccurrences(Multiset<?> superMultiset, Multiset<?> subMultiset) {
    checkNotNull(superMultiset);
    checkNotNull(subMultiset);
    for (Entry<?> entry : subMultiset.entrySet()) {

   * works better than Ordering.natural().nullsFirst() because, if null comes before all other
   * values, it lies outside the submap/submultiset ranges we test, and the variety of tests that
   * exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<@Nullable String>, Serializable {

    throw new UnsupportedOperationException();
  }

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

  @Override
  public ImmutableSortedMultiset<E> subMultiset(
      E lowerBound, BoundType lowerBoundType, E upperBound, BoundType upperBoundType) {
    checkArgument(
        comparator().compare(lowerBound, upperBound) <= 0,
        "Expected lowerBound <= upperBound but %s > %s",