@Override
        Map<K, Collection<V>> map() {
          return AsMap.this;
        }

        @Override
        public Iterator<Entry<K, Collection<V>>> iterator() {
          return new AbstractIterator<Entry<K, Collection<V>>>() {
            final Iterator<Entry<K, Collection<V>>> backingIterator =
                unfiltered.asMap().entrySet().iterator();

            @Override
            @CheckForNull

      final Iterable<? extends Optional<? extends T>> optionals) {
    checkNotNull(optionals);
    return new Iterable<T>() {
      @Override
      public Iterator<T> iterator() {
        return new AbstractIterator<T>() {
          private final Iterator<? extends Optional<? extends T>> iterator =
              checkNotNull(optionals.iterator());

          @Override
          @CheckForNull

      final Iterable<? extends Optional<? extends T>> optionals) {
    checkNotNull(optionals);
    return new Iterable<T>() {
      @Override
      public Iterator<T> iterator() {
        return new AbstractIterator<T>() {
          private final Iterator<? extends Optional<? extends T>> iterator =
              checkNotNull(optionals.iterator());

          @Override
          @CheckForNull

    }
  }

  private interface Strategy {
    Iterator<String> iterator(Splitter splitter, CharSequence toSplit);
  }

  private abstract static class SplittingIterator extends AbstractIterator<String> {
    final CharSequence toSplit;
    final CharMatcher trimmer;
    final boolean omitEmptyStrings;

    /**

    }
  }

  private interface Strategy {
    Iterator<String> iterator(Splitter splitter, CharSequence toSplit);
  }

  private abstract static class SplittingIterator extends AbstractIterator<String> {
    final CharSequence toSplit;
    final CharMatcher trimmer;
    final boolean omitEmptyStrings;

    /**

  public static <T extends @Nullable Object> UnmodifiableIterator<T> filter(
      Iterator<T> unfiltered, Predicate<? super T> retainIfTrue) {
    checkNotNull(unfiltered);
    checkNotNull(retainIfTrue);
    return new AbstractIterator<T>() {
      @Override
      @CheckForNull
      protected T computeNext() {
        while (unfiltered.hasNext()) {
          T element = unfiltered.next();
          if (retainIfTrue.apply(element)) {

  public static <T extends @Nullable Object> UnmodifiableIterator<T> filter(
      Iterator<T> unfiltered, Predicate<? super T> retainIfTrue) {
    checkNotNull(unfiltered);
    checkNotNull(retainIfTrue);
    return new AbstractIterator<T>() {
      @Override
      @CheckForNull
      protected T computeNext() {
        while (unfiltered.hasNext()) {
          T element = unfiltered.next();
          if (retainIfTrue.apply(element)) {