@GwtIncompatible
@ElementTypesAreNonnullByDefault
final class RegularImmutableSortedMultiset<E> extends ImmutableSortedMultiset<E> {
  private static final long[] ZERO_CUMULATIVE_COUNTS = {0};

  static final ImmutableSortedMultiset<?> NATURAL_EMPTY_MULTISET =
      new RegularImmutableSortedMultiset<>(Ordering.natural());

  @VisibleForTesting final transient RegularImmutableSortedSet<E> elementSet;

    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() {