@Override
    public Builder<E> addAll(Iterable<? extends E> elements) {
      if (elements instanceof Multiset) {
        Multiset<? extends E> multiset = Multisets.cast(elements);
        multiset.forEachEntry((e, n) -> contents.add(checkNotNull(e), n));
      } else {
        super.addAll(elements);
      }
      return this;
    }

    /**

    ImmutableSortedMultiset<String> multiset =
        ImmutableSortedMultiset.<String>naturalOrder().add("a").add("b").add("a").add("c").build();
    List<Multiset.Entry<String>> entries = new ArrayList<>();
    multiset.forEachEntry((e, c) -> entries.add(Multisets.immutableEntry(e, c)));
    assertThat(entries)
        .containsExactly(
            Multisets.immutableEntry("a", 2),
            Multisets.immutableEntry("b", 1),

        setCount(prevEntry.getElement(), 0);
        prevEntry = null;
      }
    };
  }

  @Override
  public void forEachEntry(ObjIntConsumer<? super E> action) {
    checkNotNull(action);
    for (AvlNode<E> node = firstNode();
        node != header && node != null && !range.tooHigh(node.getElement());
        node = node.succ()) {

  private static <E extends @Nullable Object> boolean addAllImpl(
      Multiset<E> self, Multiset<? extends E> elements) {
    if (elements.isEmpty()) {
      return false;
    }
    elements.forEachEntry(self::add);
    return true;
  }

  /** An implementation of {@link Multiset#removeAll}. */
  static boolean removeAllImpl(Multiset<?> self, Collection<?> elementsToRemove) {
    Collection<?> collection =