```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009_py39.py!}
```

Using `Optional[str]` instead of just `str` will let the editor help you detect errors where you could be assuming that a value is always a `str`, when it could actually be `None` too.

`Optional[Something]` is actually a shortcut for `Union[Something, None]`, they are equivalent.

  /*
   * The ConcurrentHashMultiset's atomic operations are implemented primarily in terms of
   * AtomicInteger's atomic operations, with some help from ConcurrentMap's atomic operations on
   * creation and removal (including automatic removal of zeroes). If the modification of an
   * AtomicInteger results in zero, we compareAndSet the value to zero; if that succeeds, we remove

          // TODO(lukes): consider building everything in terms of ListenableScheduledFuture then
          // the AbstractService could monitor the future directly. Rescheduling is still hard...
          // but it would help with some of these lock ordering issues.
          scheduleFailure = e;
          toReturn = new FutureAsCancellable(immediateCancelledFuture());
        } finally {
          lock.unlock();
        }

            throw e;
        }
    }

    private void informativeCommands(CliRequest cliRequest) throws ExitException {
        if (cliRequest.commandLine.hasOption(CLIManager.HELP)) {
            cliManager.displayHelp(System.out);
            throw new ExitException(0);
        }

        if (cliRequest.commandLine.hasOption(CLIManager.VERSION)) {

   * AtomicReferenceFieldUpdaterAtomicHelper, which would fail with a similar problem to
   * VarHandleAtomicHelperMaker, forcing us all the way to SynchronizedHelper.
   *
   * Additionally, it seems that nestmates do not help with runtime reflection under *Android*, even
   * when we use a newer -source and -target. That doesn't normally matter for AbstractFutureState,

          // TODO(lukes): consider building everything in terms of ListenableScheduledFuture then
          // the AbstractService could monitor the future directly. Rescheduling is still hard...
          // but it would help with some of these lock ordering issues.
          scheduleFailure = e;
          toReturn = new FutureAsCancellable(immediateCancelledFuture());
        } finally {
          lock.unlock();
        }

Zum Beispiel:

* <a href="https://code.visualstudio.com/docs/python/environments#_select-and-activate-an-environment" class="external-link" target="_blank">VS Code</a>
* <a href="https://www.jetbrains.com/help/pycharm/creating-virtual-environment.html" class="external-link" target="_blank">PyCharm</a>

/// tip | Tipp

Normalerweise müssen Sie dies nur **einmal** tun, wenn Sie die virtuelle Umgebung erstellen.

///

        }
        TypeVariable<?> typeVar = (TypeVariable<?>) type;
        for (AnnotatedType bound : typeVar.getAnnotatedBounds()) {
          // Until Java 15, the isNullableTypeVariable case here won't help:
          // https://bugs.openjdk.org/browse/JDK-8202469
          if (containsNullable(bound.getAnnotations()) || isNullableTypeVariable(bound.getType())) {
            return true;
          }
        }

   *
   * @since 20.0
   */
  public static final MediaType WAX_AUDIO = createConstant(AUDIO_TYPE, "x-ms-wax");

  /**
   * Real Audio. For more information, see <a
   * href="http://service.real.com/help/faq/rp8/configrp8win.html">this link</a>.
   *
   * @since 20.0
   */
  public static final MediaType VND_REAL_AUDIO = createConstant(AUDIO_TYPE, "vnd.rn-realaudio");

  /**

Check these logs for troubleshooting:

- **Main Application**: `logs/fess.log`
- **Crawler**: `logs/fess-crawler.log`
- **Search**: `logs/fess-search.log`
- **Thumbnail**: `logs/fess-thumbnail.log`

### Getting Help

- **Documentation**: https://fess.codelibs.org/
- **GitHub Issues**: https://github.com/codelibs/fess/issues
- **Discussions**: https://github.com/codelibs/fess/discussions

---

## Migration Checklist