* @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.
   */
  @SuppressWarnings("unchecked")
  public static <T> Collector<T, ?, Optional<T>> toOptional() {
    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

   * @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.
   */
  @SuppressWarnings("unchecked")
  public static <T> Collector<T, ?, Optional<T>> toOptional() {
    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

   * iterable is empty.
   *
   * <p><b>Java 8+ users:</b> the {@code Stream} equivalent to this method is {@code
   * stream.collect(MoreCollectors.toOptional()).orElse(defaultValue)}.
   *
   * @throws IllegalArgumentException if the iterator contains multiple elements
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(

   * iterable is empty.
   *
   * <p><b>Java 8+ users:</b> the {@code Stream} equivalent to this method is {@code
   * stream.collect(MoreCollectors.toOptional()).orElse(defaultValue)}.
   *
   * @throws IllegalArgumentException if the iterator contains multiple elements
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(

        for (int i = 0; i < size; i++) {
          root = Optional.of(new BinaryNode(rng.nextInt(), root, Optional.<BinaryNode>absent()));
        }
        return root;
      }
    },
    ALL_RIGHT {
      @Override
      Optional<BinaryNode> createTree(int size, Random rng) {
        Optional<BinaryNode> root = Optional.absent();
        for (int i = 0; i < size; i++) {

     *
     * @return an {@link Optional} containing the map of user properties, or empty if not set
     */
    @Nonnull
    Optional<Map<String, String>> userProperties();

    /**
     * Indicates whether to show the version information and exit.
     *
     * @return an {@link Optional} containing the boolean flag, or empty if not set
     */
    @Nonnull
    Optional<Boolean> showVersionAndExit();

    /**

     *
     * @return an {@link Optional} containing the list of goals, or empty if not specified
     */
    @Nonnull
    Optional<List<String>> goals();

    /**
     * Returns the target POM model version for upgrades.
     * Supported values include "4.0.0" and "4.1.0".
     *
     * @return an {@link Optional} containing the model version, or empty if not specified
     */
    @Nonnull

            this.scope = scope;
            return this;
        }

        public DependencyCoordinatesFactoryRequestBuilder optional(boolean optional) {
            this.optional = optional;
            return this;
        }

        public DependencyCoordinatesFactoryRequestBuilder exclusions(Collection<Exclusion> exclusions) {
            if (exclusions != null) {

    throw new IllegalStateException("Optional.get() cannot be called on an absent value");
  }

  @Override
  public T or(T defaultValue) {
    return checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");
  }

  @SuppressWarnings("unchecked") // safe covariant cast
  @Override
  public Optional<T> or(Optional<? extends T> secondChoice) {
    return (Optional<T>) checkNotNull(secondChoice);
  }

     */
    @Nonnull
    Optional<Path> rootDirectory();

    /**
     * Returns the input stream for the Maven execution, if running in embedded mode.
     *
     * @return an {@link Optional} containing the input stream, or empty if not applicable
     */
    @Nonnull
    default Optional<InputStream> stdIn() {
        return Optional.ofNullable(parserRequest().stdIn());
    }

    /**