Set<E> unfiltered, Predicate<? super E> predicate) {
    if (unfiltered instanceof SortedSet) {
      return filter((SortedSet<E>) unfiltered, predicate);
    }
    if (unfiltered instanceof FilteredSet) {
      // Support clear(), removeAll(), and retainAll() when filtering a filtered
      // collection.
      FilteredSet<E> filtered = (FilteredSet<E>) unfiltered;

      Multimap<K, V> unfiltered, Predicate<? super K> keyPredicate) {
    if (unfiltered instanceof SetMultimap) {
      return filterKeys((SetMultimap<K, V>) unfiltered, keyPredicate);
    } else if (unfiltered instanceof ListMultimap) {
      return filterKeys((ListMultimap<K, V>) unfiltered, keyPredicate);
    } else if (unfiltered instanceof FilteredKeyMultimap) {

      Multimap<K, V> unfiltered, Predicate<? super K> keyPredicate) {
    if (unfiltered instanceof SetMultimap) {
      return filterKeys((SetMultimap<K, V>) unfiltered, keyPredicate);
    } else if (unfiltered instanceof ListMultimap) {
      return filterKeys((ListMultimap<K, V>) unfiltered, keyPredicate);
    } else if (unfiltered instanceof FilteredKeyMultimap) {

    List<String> expected = emptyList();
    List<String> actual = Lists.newArrayList(filtered);
    assertEquals(expected, actual);
  }

  public void testFilterMatchAll() {
    Iterator<String> unfiltered = Lists.newArrayList("foo", "bar").iterator();
    Iterator<String> filtered = filter(unfiltered, Predicates.alwaysTrue());

    List<String> expected = emptyList();
    List<String> actual = Lists.newArrayList(filtered);
    assertEquals(expected, actual);
  }

  public void testFilterMatchAll() {
    Iterator<String> unfiltered = Lists.newArrayList("foo", "bar").iterator();
    Iterator<String> filtered = filter(unfiltered, Predicates.alwaysTrue());

        }
      }
    };
  }

  /**
   * Returns a view of {@code unfiltered} containing all elements that satisfy the input predicate
   * {@code retainIfTrue}.
   */
  public static <T extends @Nullable Object> UnmodifiableIterator<T> filter(
      Iterator<T> unfiltered, Predicate<? super T> retainIfTrue) {
    checkNotNull(unfiltered);
    checkNotNull(retainIfTrue);
    return new AbstractIterator<T>() {

        if (opLambda != null) {
            opLambda.callback(builder);
        }
    }

    public void filtered(FilteredCall<ThumbnailQueueCQ, ThumbnailQueueCQ> filteredLambda) {
        filtered(filteredLambda, null);
    }

    public void filtered(FilteredCall<ThumbnailQueueCQ, ThumbnailQueueCQ> filteredLambda, ConditionOptionCall<BoolQueryBuilder> opLambda) {

        if (opLambda != null) {
            opLambda.callback(builder);
        }
    }

    public void filtered(FilteredCall<RelatedContentCQ, RelatedContentCQ> filteredLambda) {
        filtered(filteredLambda, null);
    }

    public void filtered(FilteredCall<RelatedContentCQ, RelatedContentCQ> filteredLambda, ConditionOptionCall<BoolQueryBuilder> opLambda) {

        if (opLambda != null) {
            opLambda.callback(builder);
        }
    }

    public void filtered(FilteredCall<PathMappingCQ, PathMappingCQ> filteredLambda) {
        filtered(filteredLambda, null);
    }

    public void filtered(FilteredCall<PathMappingCQ, PathMappingCQ> filteredLambda, ConditionOptionCall<BoolQueryBuilder> opLambda) {
        bool((must, should, mustNot, filter) -> {

        if (opLambda != null) {
            opLambda.callback(builder);
        }
    }

    public void filtered(FilteredCall<WebAuthenticationCQ, WebAuthenticationCQ> filteredLambda) {
        filtered(filteredLambda, null);
    }

    public void filtered(FilteredCall<WebAuthenticationCQ, WebAuthenticationCQ> filteredLambda,
            ConditionOptionCall<BoolQueryBuilder> opLambda) {