*
 * <p>For serialization to work, the subclass must specify explicit {@code readObject} and {@code
 * writeObject} methods.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
abstract class AbstractMapBasedMultiset<E extends @Nullable Object> extends AbstractMultiset<E>
    implements Serializable {
  // TODO(lowasser): consider overhauling this back to Map<E, Integer>
  private transient Map<E, Count> backingMap;

  /*

    // It'd be nice if we could specialize for ImmutableMultiset here without also retaining
    // its code when it's not in scope...
    if (elements instanceof AbstractMapBasedMultiset) {
      return addAllImpl(self, (AbstractMapBasedMultiset<? extends E>) elements);
    } else if (elements.isEmpty()) {
      return false;
    } else {
      for (Multiset.Entry<? extends E> entry : elements.entrySet()) {