break;
                default:
                    // could not parse expression
                    return null;
            }
        }

        if (value instanceof Optional) {
            value = ((Optional<?>) value).orElse(null);
        }
        return value;
    }

    private static Object getMappedValue(

Zum Beispiel deklariert das obige Modell ein JSON "`object`" (oder Python-`dict`) wie dieses:

```JSON
{
    "name": "Foo",
    "description": "An optional description",
    "price": 45.2,
    "tax": 3.5
}
```

Da `description` und `tax` optional sind (mit `None` als Defaultwert), wäre folgendes JSON "`object`" auch gültig:

import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.DocumentUtil;
import org.codelibs.fess.util.FacetResponse;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.util.LaRequestUtil;
import org.opensearch.action.search.SearchRequestBuilder;
import org.opensearch.action.search.SearchResponse;

from dataclasses import dataclass
from datetime import datetime, timezone
from decimal import Decimal
from enum import Enum
from pathlib import PurePath, PurePosixPath, PureWindowsPath
from typing import Optional

import pytest
from fastapi._compat import PYDANTIC_V2, Undefined
from fastapi.encoders import jsonable_encoder
from pydantic import BaseModel, Field, ValidationError

## API Request Parameters

### Version

For example, this model above declares a JSON "`object`" (or Python `dict`) like:

```JSON
{
    "name": "Foo",
    "description": "An optional description",
    "price": 45.2,
    "tax": 3.5
}
```

...as `description` and `tax` are optional (with a default value of `None`), this JSON "`object`" would also be valid:

```JSON

/// note

**FastAPI** saura que la valeur de `q` n'est pas requise grâce à la valeur par défaut `=None`.

Le type `Optional` dans `Optional[str]` n'est pas utilisé par **FastAPI**, mais sera utile à votre éditeur pour améliorer le support offert par ce dernier et détecter plus facilement des erreurs de type.

///

## Sans Pydantic

          .put(TimeUnit.class, SECONDS)
          .put(Charset.class, UTF_8)
          .put(Currency.class, Currency.getInstance(Locale.US))
          .put(Locale.class, Locale.US)
          .put(Optional.class, Optional.empty())
          .put(OptionalInt.class, OptionalInt.empty())
          .put(OptionalLong.class, OptionalLong.empty())
          .put(OptionalDouble.class, OptionalDouble.empty())

 * under the License.
 */
package org.apache.maven.api.services;

import java.nio.file.Path;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Optional;

import org.apache.maven.api.Artifact;
import org.apache.maven.api.ProducedArtifact;
import org.apache.maven.api.Project;
import org.apache.maven.api.ProjectScope;
import org.apache.maven.api.RemoteRepository;

Sprich:

```Python
q: Union[str, None] = Query(default=None)
```

... macht den Parameter optional, mit dem Defaultwert `None`, genauso wie:

```Python
q: Union[str, None] = None
```

Und in Python 3.10 und darüber macht:

```Python
q: str | None = Query(default=None)
```

... den Parameter optional, mit dem Defaultwert `None`, genauso wie:

```Python
q: str | None = None
```