packages.addAll(descriptor.getExportedPackages());
                }
            }
        } catch (IOException ignored) {
            // exports descriptors are entirely optional
        }

        return new CoreExtensionEntry(loader, artifacts, packages, null, null);
    }

    public static CoreExtensionEntry discoverFrom(

from typing import Optional

import pytest
from dirty_equals import HasRepr, IsDict, IsOneOf
from fastapi import Depends, FastAPI
from fastapi.exceptions import ResponseValidationError
from fastapi.testclient import TestClient

from .utils import needs_pydanticv2


@pytest.fixture(name="client")
def get_client():
    from pydantic import BaseModel, ValidationInfo, field_validator

    app = FastAPI()

    class ModelB(BaseModel):

        ),
    ] = "https://fastapi.tiangolo.com/img/favicon.png",
    oauth2_redirect_url: Annotated[
        Optional[str],
        Doc(
            """
            The OAuth2 redirect URL, it is normally automatically handled by FastAPI.
            """
        ),
    ] = None,
    init_oauth: Annotated[
        Optional[Dict[str, Any]],
        Doc(
            """

/// tip

Prefer to use the `Annotated` version if possible.

///

```Python hl_lines="8-9"
{!> ../../docs_src/dependencies/tutorial005.py!}
```

////

It declares an optional query parameter `q` as a `str`, and then it just returns it.

This is quite simple (not very useful), but will help us focus on how the sub-dependencies work.

## Second dependency, "dependable" and "dependant"

# OkHttp test platform rules uses optional classes.

import org.codelibs.fess.mylasta.action.FessUserBean;
import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.RenderDataUtil;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.Execute;
import org.lastaflute.web.login.exception.LoginFailureException;
import org.lastaflute.web.response.HtmlResponse;

Package: fess
Version: [[version]]
Architecture: all
Maintainer: Fess Team
Depends: libc6, adduser
Section: web
Priority: optional
Homepage: https://github.com/codelibs/fess
Description: Enterprise Search Server: Fess

			<version>${project.version}</version>
		</dependency>
		<dependency>
			<groupId>org.codelibs.fess</groupId>
			<artifactId>fess-crawler-lasta</artifactId>
			<version>${project.version}</version>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>org.codelibs</groupId>
			<artifactId>corelib</artifactId>
			<version>${corelib.version}</version>
		</dependency>
		<dependency>

      return new Chopper() {
        @Override
        Optional<String> chop(String str) {
          return i.chop(str).or(you.chop(str));
        }
      };
    }

    abstract Optional<String> chop(String str);

    static Chopper suffix(String suffix) {
      return new Chopper() {
        @Override
        Optional<String> chop(String str) {
          if (str.endsWith(suffix)) {

以下のアプリケーションを例にしてみましょう:

```Python hl_lines="9"
{!../../docs_src/query_params_str_validations/tutorial001.py!}
```

クエリパラメータ `q` は `Optional[str]` 型で、`None` を許容する `str` 型を意味しており、デフォルトは `None` です。そのため、FastAPIはそれが必須ではないと理解します。

/// note | "備考"

FastAPIは、 `q` はデフォルト値が `=None` であるため、必須ではないと理解します。

`Optional[str]` における `Optional` はFastAPIには利用されませんが、エディターによるより良いサポートとエラー検出を可能にします。

///

## バリデーションの追加