testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(a.getElement(), CLOSED, a.getElement(), OPEN));
    testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(a.getElement(), OPEN, a.getElement(), OPEN));
    testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(a.getElement(), OPEN, a.getElement(), CLOSED));
    testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(b.getElement(), CLOSED, a.getElement(), CLOSED));

    testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(a.getElement(), CLOSED, a.getElement(), OPEN));
    testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(a.getElement(), OPEN, a.getElement(), OPEN));
    testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(a.getElement(), OPEN, a.getElement(), CLOSED));
    testEmptyRangeSubMultiset(
        sortedMultiset.subMultiset(b.getElement(), CLOSED, a.getElement(), CLOSED));

   * created for them.
   */
  enum NoRecurse implements Feature<Void> {
    SUBMULTISET,
    DESCENDING;

    @Override
    public Set<Feature<? super Void>> getImpliedFeatures() {
      return emptySet();
    }
  }

  /** Two bounds (from and to) define how to build a subMultiset. */
  enum Bound {
    INCLUSIVE,
    EXCLUSIVE,
    NO_BOUND;
  }

  }

  @Override
  public SortedMultiset<E> subMultiset(
      @ParametricNullness E lowerBound,
      BoundType lowerBoundType,
      @ParametricNullness E upperBound,
      BoundType upperBoundType) {
    return Multisets.unmodifiableSortedMultiset(
        delegate().subMultiset(lowerBound, lowerBoundType, upperBound, upperBoundType));
  }

  @Override

   * 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 {
    /*

   * 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 {
    /*