}

    @Override
    public @Nullable K higherKey(@ParametricNullness K key) {
      return sortedMap().higherKey(key);
    }

    @Override
    public @Nullable Entry<K, Collection<V>> firstEntry() {
      Entry<K, Collection<V>> entry = sortedMap().firstEntry();
      return (entry == null) ? null : wrapEntry(entry);
    }

    @Override

      rootReference.clear();
    } else {
      // TODO(cpovirk): Perhaps we can optimize in this case, too?
      Iterators.clear(entryIterator());
    }
  }

  private Entry<E> wrapEntry(AvlNode<E> baseEntry) {
    return new Multisets.AbstractEntry<E>() {
      @Override
      @ParametricNullness
      public E getElement() {
        return baseEntry.getElement();
      }

      rootReference.clear();
    } else {
      // TODO(cpovirk): Perhaps we can optimize in this case, too?
      Iterators.clear(entryIterator());
    }
  }

  private Entry<E> wrapEntry(AvlNode<E> baseEntry) {
    return new Multisets.AbstractEntry<E>() {
      @Override
      @ParametricNullness
      public E getElement() {
        return baseEntry.getElement();
      }