* @author Louis Wasserman
 */
@GwtCompatible
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class RegularImmutableMultiset<E> extends ImmutableMultiset<E> {
  static final RegularImmutableMultiset<Object> EMPTY =
      new RegularImmutableMultiset<>(ObjectCountHashMap.create());

  final transient ObjectCountHashMap<E> contents;
  private final transient int size;

import org.jspecify.annotations.Nullable;

/** Never actually created; instead delegates to JdkBackedImmutableMultiset. */
final class RegularImmutableMultiset<E> extends ImmutableMultiset<E> {
  static final ImmutableMultiset<Object> EMPTY =
      JdkBackedImmutableMultiset.create(ImmutableList.of());

  RegularImmutableMultiset() {}

  static <E> ImmutableMultiset<E> create(Collection<? extends Entry<? extends E>> entries) {
    if (entries.isEmpty()) {

 *
 * @author Jared Levy
 * @author Louis Wasserman
 */
@GwtCompatible
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class RegularImmutableMultiset<E> extends ImmutableMultiset<E> {
  private static final ImmutableEntry<?>[] EMPTY_ARRAY = new ImmutableEntry<?>[0];
  static final ImmutableMultiset<Object> EMPTY = create(ImmutableList.<Entry<Object>>of());

     * allocate an object for each entry, so we check for that.
     */
    static <T> @Nullable ObjectCountHashMap<T> tryGetMap(Iterable<T> multiset) {
      if (multiset instanceof RegularImmutableMultiset) {
        return ((RegularImmutableMultiset<T>) multiset).contents;
      } else if (multiset instanceof AbstractMapBasedMultiset) {
        return ((AbstractMapBasedMultiset<T>) multiset).backingMap;
      } else {

   */
  @SuppressWarnings("unchecked") // all supported methods are covariant
  public static <E> ImmutableMultiset<E> of() {
    return (ImmutableMultiset<E>) RegularImmutableMultiset.EMPTY;
  }

  /**
   * Returns an immutable multiset containing a single element.
   *
   * @throws NullPointerException if the element is null
   * @since 6.0 (source-compatible since 2.0)
   */