checkNotNull(supplier);
    return reference;
  }

  @Override
  public T orNull() {
    return reference;
  }

  @Override
  public Set<T> asSet() {
    return Collections.singleton(reference);
  }

  @Override
  public <V> Optional<V> transform(Function<? super T, V> function) {
    return new Present<>(
        checkNotNull(
            function.apply(reference),

    multiset.add(checkNotNull(elementFunction.apply(t)), countFunction.applyAsInt(t));
  }

  /**
   * Returns the empty immutable sorted multiset.
   *
   * <p><b>Performance note:</b> the instance returned is a singleton.
   */
  @SuppressWarnings("unchecked")
  public static <E> ImmutableSortedMultiset<E> of() {
    return (ImmutableSortedMultiset) RegularImmutableSortedMultiset.NATURAL_EMPTY_MULTISET;
  }

    synchronized void addEdge(String from, String to) throws CycleDetectedException {
        if (graph.computeIfAbsent(from, l -> new HashSet<>()).add(to)) {
            List<String> cycle = visitCycle(graph, Collections.singleton(to), new HashMap<>(), new LinkedList<>());
            if (cycle != null) {
                // remove edge which introduced cycle
                throw new CycleDetectedException(

            String relativePath = adocDir.relativize(adocFile.toPath()).toString();
            File docInfo = new File(destinationDirectory, docInfoName);
            try {
                Files.write(docInfo.toPath(), Collections.singleton(String.format("<meta name=\"adoc-src-path\" content=\"%s\">", relativePath)), StandardOpenOption.CREATE);
            } catch (IOException e) {
                throw UncheckedException.throwAsUncheckedException(e);
            }

    @Test
    void testMNG4738() throws Exception {
        Artifact g = createLocalArtifact("g", "1.0");
        createLocalArtifact("h", "1.0");
        artifactResolver.resolveTransitively(
                Collections.singleton(g), projectArtifact, remoteRepositories(), localRepository(), null);

        // we want to see all top-level thread groups
        ThreadGroup tg = Thread.currentThread().getThreadGroup();

      for (BoundType boundType : BoundType.values()) {
        queryBuilder.add(Range.upTo(i, boundType));
        queryBuilder.add(Range.downTo(i, boundType));
      }
      queryBuilder.add(Range.singleton(i));
      queryBuilder.add(Range.openClosed(i, i));
      queryBuilder.add(Range.closedOpen(i, i));

      for (BoundType lowerBoundType : BoundType.values()) {
        for (int j = i + 1; j <= MAX_BOUND; j++) {

    }

    private ArtifactResolutionResult collect(ArtifactSpec a) throws ArtifactResolutionException {
        return artifactCollector.collect(
                Collections.singleton(a.artifact),
                projectArtifact.artifact,
                null,
                null,
                null,
                source,
                null,
                Collections.emptyList(),

   */
  protected IteratorTester(
      int steps,
      Iterable<? extends IteratorFeature> features,
      Iterable<E> expectedElements,
      KnownOrder knownOrder) {
    super(steps, Collections.singleton(null), features, expectedElements, knownOrder, 0);
  }

  @Override
  protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
    return iteratorStimuli();
  }

   */
  protected IteratorTester(
      int steps,
      Iterable<? extends IteratorFeature> features,
      Iterable<E> expectedElements,
      KnownOrder knownOrder) {
    super(steps, Collections.singleton(null), features, expectedElements, knownOrder, 0);
  }

  @Override
  protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
    return iteratorStimuli();
  }

                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    suite.addTestSuite(ImmutableSortedSetTest.class);

    return suite;
  }

  // enum singleton pattern
  private enum StringLengthComparator implements Comparator<String> {
    INSTANCE;

    @Override
    public int compare(String a, String b) {
      return a.length() - b.length();
    }
  }