*/
    @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());
    }

    /**

    }

    @Override
    public Optional<Project> getProject() {
        return Optional.ofNullable(session.getProject(delegate.getProject()));
    }

    @Override
    public Optional<MojoExecution> getMojoExecution() {
        return Optional.ofNullable(delegate.getMojoExecution()).map(me -> new DefaultMojoExecution(session, me));
    }

    @Override
    public Optional<Exception> getException() {

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

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

            @Nonnull

     *
     * @return an {@link Optional} containing the boolean value {@code true} if specified, or empty
     */
    Optional<Boolean> force();

    /**
     * Should imply "yes" to all questions.
     *
     * @return an {@link Optional} containing the boolean value {@code true} if specified, or empty
     */
    Optional<Boolean> yes();

    /**

        // v1 == 0.
        .optional(defaultValue = 0),
      Adapters.INTEGER_AS_BIG_INTEGER,
      algorithmIdentifier,
      name,
      validity,
      name,
      subjectPublicKeyInfo,
      Adapters.BIT_STRING.withTag(tag = 1L).optional(),
      Adapters.BIT_STRING.withTag(tag = 2L).optional(),
      extension.asSequenceOf().withExplicitBox(tag = 3).optional(defaultValue = listOf()),
      decompose = {

            throw new LookupException(e);
        }
    }

    @Override
    public <T> Optional<T> lookupOptional(Class<T> type) {
        try {
            return Optional.of(container.lookup(type));
        } catch (ComponentLookupException e) {
            if (e.getCause() instanceof NoSuchElementException) {
                return Optional.empty();
            }
            throw new LookupException(e);
        }
    }

Voici un conseil issu de mon point de vue très subjectif :

- 🚨 Évitez d'utiliser `Optional[SomeType]`
- À la place ✨ **utilisez `Union[SomeType, None]`** ✨.

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

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

  @Override
  public Optional<T> or(Optional<? extends T> secondChoice) {
    checkNotNull(secondChoice);
    return this;
  }

  @Override
  public T or(Supplier<? extends T> supplier) {

两者是等价的，底层其实也是一样的。但我更推荐使用 `Union` 而不是 `Optional`，因为单词“optional”（可选）看起来会暗示该值是可选的，而它真正的含义是“它可以是 `None`”，即使它并不是可选的，仍然是必填的。

我认为 `Union[SomeType, None]` 更能明确表达其含义。

这只是关于词语和命名的问题，但这些词语会影响你和你的队友如何看待代码。

举个例子，看这段函数：

```python
from typing import Optional


def say_hi(name: Optional[str]):
    print(f"Hey {name}!")
```

参数 `name` 被定义为 `Optional[str]`，但它并不是“可选”的，你不能不传这个参数就调用函数：

```Python

@REM
@REM   JAVA_HOME           (Optional) Points to a Java installation.
@REM   MAVEN_BATCH_ECHO    (Optional) Set to 'on' to enable the echoing of the batch commands.
@REM   MAVEN_BATCH_PAUSE   (Optional) set to 'on' to wait for a key stroke before ending.
@REM   MAVEN_OPTS          (Optional) Java runtime options used when Maven is executed.
@REM   MAVEN_SKIP_RC       (Optional) Flag to disable loading of mavenrc files.