}

  private static final Function<Object, Optional<?>> NULLABLE_TO_OPTIONAL =
      new Function<Object, Optional<?>>() {
        @Override
        public Optional<?> apply(@Nullable Object obj) {
          return Optional.fromNullable(obj);
        }
      };

  private static final Function<Optional<?>, @Nullable Object> OPTIONAL_TO_NULLABLE =
      new Function<Optional<?>, @Nullable Object>() {
        @Override

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

    /**
     * Indicates whether Maven should suppress SNAPSHOT updates.
     *
     * @return an {@link Optional} containing true if SNAPSHOT updates should be suppressed, false if not, or empty if not specified
     */
    @Nonnull

     *
     * @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();

    /**

        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++) {

        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++) {

    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);
  }

  public void testEmptiesFirst() {
    Optional<String> empty = Optional.empty();
    Optional<String> abc = Optional.of("abc");
    Optional<String> z = Optional.of("z");

    Comparator<Optional<String>> comparator = emptiesFirst(comparing(String::length));
    testComparator(comparator, empty, z, abc);

    // Just demonstrate that no explicit type parameter is required
    Comparator<Optional<String>> unused = emptiesFirst(naturalOrder());

     *
     * @return An Optional containing the lowest matching version, or empty Optional if no versions
     *         matched the requested range
     */
    @Nonnull
    default Optional<Version> getLowestVersion() {
        return getVersions().isEmpty()
                ? Optional.empty()
                : Optional.of(getVersions().get(0));
    }

    /**

     *
     * @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

     */
    @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());
    }

    /**