collection.clear();
      totalSize -= count;
    }
  }

  private abstract class Itr<T extends @Nullable Object> implements Iterator<T> {
    final Iterator<Entry<K, Collection<V>>> keyIterator;
    @CheckForNull K key;
    @CheckForNull Collection<V> collection;
    Iterator<V> valueIterator;

    Itr() {
      keyIterator = map.entrySet().iterator();
      key = null;
      collection = null;

      collection.clear();
      totalSize -= count;
    }
  }

  private abstract class Itr<T extends @Nullable Object> implements Iterator<T> {
    final Iterator<Entry<K, Collection<V>>> keyIterator;
    @CheckForNull K key;
    @CheckForNull Collection<V> collection;
    Iterator<V> valueIterator;

    Itr() {
      keyIterator = map.entrySet().iterator();
      key = null;
      collection = null;