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

        return incidentNodes(edge).adjacentNode(nodePresent).equals(nodeToCheck);
      }
    };
  }

  @Override
  public Optional<E> edgeConnecting(N nodeU, N nodeV) {
    return Optional.ofNullable(edgeConnectingOrNull(nodeU, nodeV));
  }

  @Override
  public Optional<E> edgeConnecting(EndpointPair<N> endpoints) {
    validateEndpoints(endpoints);
    return edgeConnecting(endpoints.nodeU(), endpoints.nodeV());

 */

package com.google.common.io;

import static com.google.common.collect.ImmutableList.toImmutableList;
import static java.nio.charset.StandardCharsets.UTF_8;

import com.google.common.base.Optional;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.io.SourceSinkFactory.ByteSourceFactory;
import com.google.common.io.SourceSinkFactory.CharSourceFactory;

```console
$ pip install "fastapi[standard]"

---> 100%
```

</div>

/// note

When you install with `pip install "fastapi[standard]"` it comes with some default optional standard dependencies.

If you don't want to have those optional dependencies, you can instead install `pip install fastapi`.

///

## Advanced User Guide

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;

/**

### Without `standard` Dependencies

If you don't want to include the `standard` optional dependencies, you can install with `pip install fastapi` instead of `pip install "fastapi[standard]"`.

### Additional Optional Dependencies

There are some additional dependencies you might want to install.

Additional optional Pydantic dependencies:

   ** <(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}})

      description: |
        Please describe the problem as concisely as possible.
    validations:
      required: true
  - type: textarea
    id: context
    attributes:
      label: Context (optional)
      description: |
        How has this issue affected you? What are you trying to accomplish?
        Providing context helps us come up with a solution that is most useful in the real world
    validations:

        // As a side effect it will log the optional projects that could not be resolved.
        projectSelector.getOptionalProjectsBySelectors(request, session.getAllProjects(), allOptionalSelectors);
    }

    /**
     * Check whether any of the requested optional profiles were not activated or deactivated.
     * @param session the Maven session.
     * @param profileActivation the requested optional and required profiles.
     */

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

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

    private static Object getMappedValue(