<div class="screenshot">
<img src="/img/tutorial/separate-openapi-schemas/image02.png">
</div>

This means that it will **always have a value**, it's just that sometimes the value could be `None` (or `null` in JSON).

            }
        }
        return OptionalObject.empty();
    }

    @Override
    public OptionalThing<Locale> getRequestedLocale(final RequestManager requestManager) {
        return OptionalObject.empty(); // means browser default
    }

    // ===================================================================================
    //                                                                      Basic Override

       - The compressed index.xml file contains a timestamp property which
       changes with every test execution, such that running the test
       actually changes the test classpath itself. This means that it
       can"t benefit from incremental build acceleration, because on every
       execution it sees that the classpath has changed, and so to be
       safe, it needs to re-run.

///

### What is "Mounting" { #what-is-mounting }

"Mounting" means adding a complete "independent" application in a specific path, that then takes care of handling all the sub-paths.

{* ../../docs_src/response_model/tutorial001_01_py310.py hl[16,21] *}

FastAPI will use this return type to:

* **Validate** the returned data.
    * If the data is invalid (e.g. you are missing a field), it means that *your* app code is broken, not returning what it should, and it will return a server error instead of returning incorrect data. This way you and your clients can be certain that they will receive the data and the data shape expected.

  // 1. In the listener that performs the callback. In this case it is fine since inputFuture is
  //    assigned prior to calling addListener, and addListener happens-before any invocation of the
  //    listener. Notably, this means that 'volatile' is unnecessary to make 'inputFuture' visible
  //    to the listener.
  //
  // 2. In done() where we may propagate cancellation to the input. In this case it is _not_ fine.

 * the specific service interface being implemented.
 * <p>
 * All SPI services should be annotated with {@link Consumer} to indicate they are meant to be
 * implemented by plugins and extensions rather than used by them.
 *
 * @since 4.0.0
 */
@Experimental
@Consumer

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- **Navigation CodeLens** — Liens cliquables au-dessus des appels du client de test (par ex. `client.get('/items')`) menant au *chemin d'accès* correspondant, pour naviguer rapidement entre les tests et l’implémentation.
- **Déployer sur FastAPI Cloud** — Déploiement en un clic de votre application sur [FastAPI Cloud](https://fastapicloud.com/).

     * <groupId>:<artifactId>:<version>} but some of these coordinates may still be unknown at the point the exception
     * is thrown so this information is merely meant to assist the user.
     *
     * @return the identifier of the project or an empty string if not known, never {@code null}
     */
    @Nonnull
    String getProjectId();

    /**