*/
@DoNotMock("Use Optional.of(value) or Optional.absent()")
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
public abstract class Optional<T> implements Serializable {
  /**
   * Returns an {@code Optional} instance with no contained reference.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {

 */
@DoNotMock("Use Optional.of(value) or Optional.absent()")
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
public abstract class Optional<T> implements Serializable {
  /**
   * Returns an {@code Optional} instance with no contained reference.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {

  }

  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

    assertThat(Optional.presentInstances(optionals)).isEmpty();
  }

  public void testPresentInstances_somePresent() {
    List<Optional<String>> optionals =
        ImmutableList.of(Optional.of("a"), Optional.<String>absent(), Optional.of("c"));
    assertThat(Optional.presentInstances(optionals)).containsExactly("a", "c").inOrder();
  }

    assertTrue(Comparators.isInStrictOrder(Collections.<Integer>emptyList(), Ordering.natural()));
  }

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

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

            }

            @Nonnull
            @Override
            public Optional<Source> getGlobalToolchainsSource() {
                return Optional.ofNullable(globalToolchainsSource);
            }

            @Nonnull
            @Override
            public Optional<Source> getUserToolchainsSource() {
                return Optional.ofNullable(userToolchainsSource);
            }
        }
    }

    assertThat(Optional.presentInstances(optionals)).isEmpty();
  }

  public void testPresentInstances_somePresent() {
    List<Optional<String>> optionals =
        ImmutableList.of(Optional.of("a"), Optional.<String>absent(), Optional.of("c"));
    assertThat(Optional.presentInstances(optionals)).containsExactly("a", "c").inOrder();
  }

    @Override
    public Path getRootDirectory() {
        return project.getRootDirectory();
    }

    @Override
    public Optional<Project> getParent() {
        MavenProject parent = project.getParent();
        return parent != null ? Optional.of(session.getProject(parent)) : Optional.empty();
    }

    @Nonnull
    private DependencyCoordinate toDependency(org.apache.maven.api.model.Dependency dependency) {

    BeanConfigurationRequest setClassLoader(ClassLoader classLoader);

    /**
     * Gets the optional preprocessor for configuration values.
     *
     * @return The preprocessor for configuration values or {@code null} if none.
     */
    BeanConfigurationValuePreprocessor getValuePreprocessor();

    /**
     * Sets the optional preprocessor for configuration values.
     *

                    .collect(Collectors.toMap(t -> t.id(), t -> t));
        }

        @Override
        public Optional<T> lookup(String id) {
            return Optional.ofNullable(values.get(id));
        }
    }