KeySet(final Map<K, Collection<V>> subMap) {
      super(subMap);
    }

    @Override
    public Iterator<K> iterator() {
      final Iterator<Entry<K, Collection<V>>> entryIterator = map().entrySet().iterator();
      return new Iterator<K>() {
        @CheckForNull Entry<K, Collection<V>> entry;

        @Override
        public boolean hasNext() {

    Collection<V> getDelegate() {
      return delegate;
    }

    @Override
    public Iterator<V> iterator() {
      refreshIfEmpty();
      return new WrappedIterator();
    }

    /** Collection iterator for {@code WrappedCollection}. */
    class WrappedIterator implements Iterator<V> {
      final Iterator<V> delegateIterator;
      final Collection<V> originalDelegate = delegate;

      WrappedIterator() {