*
   * @throws NullPointerException if any of {@code elements} is null
   */
  public static <E> ImmutableMultiset<E> copyOf(Iterable<? extends E> elements) {
    if (elements instanceof ImmutableMultiset) {
      @SuppressWarnings("unchecked") // all supported methods are covariant
      ImmutableMultiset<E> result = (ImmutableMultiset<E>) elements;
      if (!result.isPartialView()) {
        return result;
      }
    }

  public void testSerialization_asList() {
    ImmutableMultiset<String> multiset = ImmutableMultiset.of("a", "a", "b", "b", "b");
    SerializableTester.reserializeAndAssert(multiset.asList());
  }

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(ImmutableMultiset.of(), ImmutableMultiset.of())
        .addEqualityGroup(ImmutableMultiset.of(1), ImmutableMultiset.of(1))

          .put(
              SortedSetMultimap.class,
              Multimaps.unmodifiableSortedSetMultimap(TreeMultimap.create()))
          .put(Multiset.class, ImmutableMultiset.of())
          .put(ImmutableMultiset.class, ImmutableMultiset.of())
          .put(SortedMultiset.class, ImmutableSortedMultiset.of())
          .put(ImmutableSortedMultiset.class, ImmutableSortedMultiset.of())

  public void testSerialization_asList() {
    ImmutableMultiset<String> multiset = ImmutableMultiset.of("a", "a", "b", "b", "b");
    SerializableTester.reserializeAndAssert(multiset.asList());
  }

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(ImmutableMultiset.of(), ImmutableMultiset.of())
        .addEqualityGroup(ImmutableMultiset.of(1), ImmutableMultiset.of(1))

    Multiset<String> mod = HashMultiset.create();
    Multiset<String> unmod = unmodifiableMultiset(mod);
    assertNotSame(mod, unmod);
    assertSame(unmod, unmodifiableMultiset(unmod));
    ImmutableMultiset<String> immutable = ImmutableMultiset.of("a", "a", "b", "a");
    assertSame(immutable, unmodifiableMultiset(immutable));
    assertSame(immutable, unmodifiableMultiset((Multiset<String>) immutable));
  }

    assertEquals(ImmutableSortedMap.of(), ArbitraryInstances.get(ImmutableSortedMap.class));
    assertEquals(ImmutableMultiset.of(), ArbitraryInstances.get(Multiset.class));
    assertEquals(ImmutableMultiset.of(), ArbitraryInstances.get(ImmutableMultiset.class));
    assertTrue(ArbitraryInstances.get(SortedMultiset.class).isEmpty());
    assertEquals(ImmutableMultimap.of(), ArbitraryInstances.get(Multimap.class));

  }

  /**
   * Returns an {@code ImmutableMultiset} containing all of the elements from this fluent iterable.
   *
   * <p><b>{@code Stream} equivalent:</b> {@code ImmutableMultiset.copyOf(stream.iterator())}, or
   * pass {@link ImmutableMultiset#toImmutableMultiset} to {@code stream.collect()}.
   *
   * @throws NullPointerException if any element is null

 * @since 12.0
 */
@GwtIncompatible // hasn't been tested yet
public abstract class ImmutableSortedMultiset<E> extends ImmutableMultiset<E>
    implements SortedMultiset<E> {
  // TODO(lowasser): GWT compatibility

  /**
   * Returns a {@code Collector} that accumulates the input elements into a new {@code
   * ImmutableMultiset}. Elements are sorted by the specified comparator.
   *

      Collector<Range<E>, ?, ImmutableRangeSet<E>> toImmutableRangeSet() {
    return (Collector) TO_IMMUTABLE_RANGE_SET;
  }

  // Multisets

  static <T extends @Nullable Object, E> Collector<T, ?, ImmutableMultiset<E>> toImmutableMultiset(
      Function<? super T, ? extends E> elementFunction, ToIntFunction<? super T> countFunction) {
    checkNotNull(elementFunction);
    checkNotNull(countFunction);
    return Collector.of(

      Collector<Range<E>, ?, ImmutableRangeSet<E>> toImmutableRangeSet() {
    return (Collector) TO_IMMUTABLE_RANGE_SET;
  }

  // Multisets

  static <T extends @Nullable Object, E> Collector<T, ?, ImmutableMultiset<E>> toImmutableMultiset(
      Function<? super T, ? extends E> elementFunction, ToIntFunction<? super T> countFunction) {
    checkNotNull(elementFunction);
    checkNotNull(countFunction);
    return Collector.of(