return false;
  }

  /** An implementation of {@link Multiset#addAll}. */
  static <E extends @Nullable Object> boolean addAllImpl(
      Multiset<E> self, Collection<? extends E> elements) {
    checkNotNull(self);
    checkNotNull(elements);
    if (elements instanceof Multiset) {
      return addAllImpl(self, cast(elements));
    } else if (elements.isEmpty()) {
      return false;
    } else {