以下のアプリケーションを例にしてみましょう:

{* ../../docs_src/query_params_str_validations/tutorial001.py hl[9] *}

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

   * properties, including:
   *
   * <ul>
   *   <li>{@code java.vendor.version} (added in Java 11, listed as optional as of Java 13)
   *   <li>{@code jdk.module.*} (added in Java 9, optional)
   * </ul>
   */
  public @Nullable String value() {
    return System.getProperty(key);
  }

  /** Returns a string representation of this system property. */

import static java.lang.reflect.Modifier.PRIVATE;
import static java.lang.reflect.Modifier.PROTECTED;
import static java.lang.reflect.Modifier.PUBLIC;
import static java.util.Arrays.asList;

import com.google.common.base.Optional;
import com.google.common.reflect.ClassPath;
import com.google.common.reflect.ClassPath.ClassInfo;
import com.google.common.reflect.TypeToken;
import java.lang.reflect.Method;
import junit.framework.TestCase;

Zum Beispiel deklariert das obige Modell ein JSON „`object`“ (oder Python-<abbr title="Dictionary – Zuordnungstabelle: In anderen Sprachen auch Hash, Map, Objekt, Assoziatives Array genannt">`dict`</abbr>) wie dieses:

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

 * under the License.
 */
package org.apache.maven.cling.invoker;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Objects;
import java.util.Optional;

import org.apache.maven.api.cli.CoreExtensions;
import org.apache.maven.api.cli.InvokerRequest;
import org.apache.maven.api.cli.extensions.CoreExtension;
import org.apache.maven.api.cli.extensions.InputLocation;

/**
 * The Extractor interface defines methods for extracting text data from an input stream.
 * Implementations of this interface should provide the logic for extracting text and
 * optionally override the default weight value.
 */
public interface Extractor {

    /**
     * Extracts text data from the given input stream.
     *
     * @param in the input stream to extract text from

MinIO implements an S3 extension to the [PostUpload](https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html) where in a special fan-out list is sent along with the TSB's for MinIO make multiple uploads from a single source stream. Optionally supports custom metadata, tags and other retention settings. All objects are also readable independently once upload is completed via the regular S3 [GetObject](https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetObject.html) API.

import org.codelibs.fess.opensearch.user.exentity.User;
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.response.HtmlResponse;
import org.lastaflute.web.response.render.RenderData;

# OkHttp test platform rules uses optional classes.

import org.codelibs.fess.opensearch.config.exentity.ScheduledJob;
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.response.HtmlResponse;
import org.lastaflute.web.response.render.RenderData;