if (strValue == null || strValue.isEmpty()) {
            return false;
        }

        if (isIgnoredProperty(strValue)) {
            return false;
        }

        // for declaration like @Parameter( property = "config.property" )
        // the value will contain ${config.property}

        try {
            return expressionEvaluator.evaluate(strValue) != null;

To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

{* ../../docs_src/openapi_callbacks/tutorial001_py310.py hl[14:16,19:20,26:30] *}

///

## Duplicate headers { #duplicate-headers }

It is possible to receive duplicate headers. That means, the same header with multiple values.

You can define those cases using a list in the type declaration.

You will receive all the values from the duplicate header as a Python `list`.

For example, to declare a header of `X-Token` that can appear more than once, you can write:

   * explicit {@code @Nullable} annotation (see <a
   * href="https://github.com/google/guava/issues/1819">#1819</a>).
   *
   * <p>It is not necessary to consider visibility, return type, or type parameter declarations. The
   * declaration of a method with the same name and formal parameters as {@link Object#equals} that
   * is not public and boolean-returning, or that declares any type parameters, would be rejected at
   * compile-time.
   */

Cela vous donne beaucoup de flexibilité. Vous pouvez retourner n'importe quel type de données, surcharger n'importe quelle déclaration ou validation de données.

## Utiliser le `jsonable_encoder` dans une `Response`

    }
  }

  /**
   * Returns a new {@link TypeVariable} that belongs to {@code declaration} with {@code name} and
   * {@code bounds}.
   */
  static <D extends GenericDeclaration> TypeVariable<D> newArtificialTypeVariable(
      D declaration, String name, Type... bounds) {
    return newTypeVariableImpl(
        declaration, name, (bounds.length == 0) ? new Type[] {Object.class} : bounds);
  }

///

## Inclure un paramètre imbriqué dans le body

Disons que vous avez seulement un paramètre `item` dans le body, correspondant à un modèle Pydantic `Item`.

Par défaut, **FastAPI** attendra sa déclaration directement dans le body.

It won't do any data conversion with Pydantic models, it won't convert the contents to any type, etc.

This gives you a lot of flexibility. You can return any data type, override any data declaration or validation, etc.

## Using the `jsonable_encoder` in a `Response` { #using-the-jsonable-encoder-in-a-response }

   * explicit {@code @NullableDecl} annotation (see <a
   * href="https://github.com/google/guava/issues/1819">#1819</a>).
   *
   * <p>It is not necessary to consider visibility, return type, or type parameter declarations. The
   * declaration of a method with the same name and formal parameters as {@link Object#equals} that
   * is not public and boolean-returning, or that declares any type parameters, would be rejected at
   * compile-time.
   */

* «the coverage»: «Die Testabdeckung»
* «the command line interface»: «Das Kommandozeileninterface»
* «the default value»: «der Defaultwert»
* «the default value»: NOT «der Standardwert»
* «the default declaration»: «die Default-Deklaration»
* «the deployment»: «das Deployment»
* «the dict»: «das Dict»
* «the dictionary»: «das Dictionary»
* «the enumeration»: «die Enumeration»
* «the enum»: «das Enum»
* «the engine»: «die Engine»