if (Ordering.natural().equals(comparator)) {
      return (ImmutableSortedMultiset<E>) RegularImmutableSortedMultiset.NATURAL_EMPTY_MULTISET;
    } else {
      return new RegularImmutableSortedMultiset<>(comparator);
    }
  }

  ImmutableSortedMultiset() {}

  @Override
  public final Comparator<? super E> comparator() {

    if (Ordering.natural().equals(comparator)) {
      return (ImmutableSortedMultiset<E>) RegularImmutableSortedMultiset.NATURAL_EMPTY_MULTISET;
    } else {
      return new RegularImmutableSortedMultiset<>(comparator);
    }
  }

  ImmutableSortedMultiset() {}

  @Override
  public final Comparator<? super E> comparator() {

    assertEquals(HashMultiset.create(asList("a", "b", "a", "c", "c")), multiset2);
    assertTrue(
        ((RegularImmutableList<String>)
                    ((RegularImmutableSortedMultiset<String>) multiset1).elementSet.elements)
                .array
            != builder.elements);
  }

  public void testBuilderAddAll() {
    List<String> a = asList("a", "b");