*/
    @Size(max = 10000)
    @Required
    public String rt;

    /**
     * Hash value for security or validation purposes.
     * This field is optional and used for request verification.
     */
    public String hash;

    /**
     * Query identifier associated with the search that led to this document access.

   ** <(optional)> reports configuration: <<<ReportConfigurationExpander>>> ({{{./apidocs/org/apache/maven/model/plugin/ReportConfigurationExpander.html}javadoc}}),
   with its <<<DefaultReportConfigurationExpander>>> implementation
   ({{{./xref/org/apache/maven/model/plugin/DefaultReportConfigurationExpander.html}source}})

    return pickInstance(Currency.getAvailableCurrencies(), Currency.getInstance(Locale.US));
  }

  @Empty
  <T> Optional<T> generateJavaOptional() {
    return Optional.empty();
  }

  @Generates
  <T> Optional<T> generateJavaOptional(T value) {
    return Optional.of(value);
  }

  @Generates
  OptionalInt generateOptionalInt() {
    return OptionalInt.of(generateInt());
  }

本例中，查询参数 `q` 是可选的，默认值为 `None`。

/// check | 检查

注意，**FastAPI** 可以识别出 `item_id` 是路径参数，`q` 不是路径参数，而是查询参数。

///

/// note | 笔记

因为默认值为 `= None`，FastAPI 把 `q` 识别为可选参数。

FastAPI 不使用 `Optional[str]` 中的 `Optional`（只使用 `str`），但 `Optional[str]` 可以帮助编辑器发现代码中的错误。

///

## 查询参数类型转换

参数还可以声明为 `bool` 类型，FastAPI 会自动转换参数类型：


{* ../../docs_src/query_params/tutorial003_py310.py hl[7] *}

本例中，访问：

```

   * implementations.
   */
  SUPPORTS_SET;

  /**
   * A set containing none of the optional features of the {@link Iterator} or {@link ListIterator}
   * interfaces.
   */
  public static final Set<IteratorFeature> UNMODIFIABLE = emptySet();

  /**
   * A set containing all of the optional features of the {@link Iterator} and {@link ListIterator}
   * interfaces.
   */

                        .nonRecursive()
                        .expectResult(MODULE_C),
                scenario("Selected optional project")
                        .activeOptionalProjects(MODULE_B)
                        .expectResult(MODULE_B),
                scenario("Selected missing optional project")
                        .activeOptionalProjects("non-existing-module")
                        .expectResult(

     * @see org.apache.maven.api.services.ArtifactManager#getPath(Artifact)
     */
    @Nonnull
    default Optional<ProducedArtifact> getMainArtifact() {
        List<ProducedArtifact> artifacts = getArtifacts();
        return artifacts.size() == 2 ? Optional.of(artifacts.get(1)) : Optional.empty();
    }

    /**

			Key:         config.SubnetSubSys,
			Type:        "string",
			Description: "register Enterprise license for the cluster",
			Optional:    true,
		},
		config.HelpKV{
			Key:         config.CallhomeSubSys,
			Type:        "string",
			Description: "enable callhome to MinIO SUBNET",
			Optional:    true,
		},
		config.HelpKV{
			Key:         config.DriveSubSys,
			Description: "enable drive specific settings",
		},

import org.codelibs.fess.opensearch.config.exentity.WebConfig;
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;

                        }
                    }
                    boolean optional = false;
                    if (!selector.isEmpty() && selector.charAt(0) == '?') {
                        optional = true;
                        selector = selector.substring(1);
                    }
                    projectActivation.addProjectActivation(selector, active, optional);
                }
            }
        }
    }