final Iterator<? extends Entry<K, ? extends ImmutableCollection<V>>> asMapItr =
          map.entrySet().iterator();
      @CheckForNull K currentKey = null;
      Iterator<V> valueItr = Iterators.emptyIterator();

      @Override
      public boolean hasNext() {
        return valueItr.hasNext() || asMapItr.hasNext();
      }

      @Override
      public Entry<K, V> next() {

      final Iterator<? extends Entry<K, ? extends ImmutableCollection<V>>> asMapItr =
          map.entrySet().iterator();
      @CheckForNull K currentKey = null;
      Iterator<V> valueItr = Iterators.emptyIterator();

      @Override
      public boolean hasNext() {
        return valueItr.hasNext() || asMapItr.hasNext();
      }

      @Override
      public Entry<K, V> next() {