クエリパラメータの宣言と同様に、モデル属性がデフォルト値をもつとき、必須な属性ではなくなります。それ以外は必須になります。オプショナルな属性にしたい場合は `None` を使用してください。

例えば、上記のモデルは以下の様なJSON「`オブジェクト`」(もしくはPythonの `dict` ) を宣言しています:

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

...`description` と `tax` はオプショナル (デフォルト値は `None`) なので、以下のJSON「`オブジェクト`」も有効です:

```JSON
{
    "name": "Foo",
    "price": 45.2

  }

  /**
   * Invokes {@code future.}{@link Future#get() get()} uninterruptibly.
   *
   * <p>Similar methods:
   *
   * <ul>
   *   <li>To retrieve a result from a {@code Future} that is already done, use {@link
   *       Futures#getDone Futures.getDone}.
   *   <li>To treat {@link InterruptedException} uniformly with other exceptions, use {@link
   *       Futures#getChecked(Future, Class) Futures.getChecked}.

			go func(disk StorageAPI) {
				defer wg.Done()
				er.cleanupStaleUploadsOnDisk(ctx, disk)
			}(disk)
		}
	}
	wg.Wait()
}

func (er erasureObjects) deleteAll(ctx context.Context, bucket, prefix string) {
	var wg sync.WaitGroup
	for _, disk := range er.getDisks() {
		if disk == nil {
			continue
		}
		wg.Add(1)
		go func(disk StorageAPI) {
			defer wg.Done()

    internal var eventListenerFactory: EventListener.Factory = EventListener.NONE.asFactory()
    internal var retryOnConnectionFailure = true
    internal var fastFallback = true
    internal var authenticator: Authenticator = Authenticator.NONE
    internal var followRedirects = true
    internal var followSslRedirects = true

     * the query term is converted to lowercase for case-insensitive matching.
     *
     * @param query the search term to find related queries for
     * @return an array of related query strings, or empty array if none found
     */
    public String[] getRelatedQueries(final String query) {
        final String key = ComponentUtil.getVirtualHostHelper().getVirtualHostKey();
        final Map<String, String[]> map = relatedQueryMap.get(key);

```Python
print(user_dict)
```

obtendremos un `dict` de Python con:

```Python
{
    'username': 'john',
    'password': 'secret',
    'email': '******@****.***',
    'full_name': None,
}
```

#### Desempaquetando un `dict` { #unpacking-a-dict }

#### `Optional`

`Optional` bir değişkenin `str`gibi bir tipi olabileceğini ama isteğe bağlı olarak tipinin `None` olabileceğini belirtir:

```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009.py!}
```

`str` yerine `Optional[str]` kullanmak editorün bu değerin her zaman `str` tipinde değil bazen `None` tipinde de olabileceğini belirtir ve hataları tespit etmemizde yardımcı olur.

#### Generic tipler

	AssertEqual(t, result3, namedUser)

	var result4 NamedUser
	if err := DB.Raw("SELECT * FROM named_users WHERE name1 = @name OR name2 = @name2 OR name3 = @name", sql.Named("name", "jinzhu-none"), sql.Named("name2", "jinzhu2")).Find(&result4).Error; err != nil {
		t.Errorf("failed to update with named arg")
	}

	AssertEqual(t, result4, namedUser)

    echo \"Failed attempts: $ATTEMPTS\" ;
    if [ $ATTEMPTS -gt $LIMIT ]; then
      exit 1 ;
    fi ;
    sleep 2 ; # 2 second intervals between attempts
    $MC_COMMAND ;
    STATUS=$? ;
  done ;
  set -e ; # reset `e` as active
  return 0
}

# checkSvcacctExists ()
# Check if the svcacct exists, by using the exit code of `mc admin user svcacct info`
checkSvcacctExists() {

    private val execOps: ExecOperations,
    private val fsOps: FileSystemOperations,
    private val fileOps: FileOperations
) : DefaultTask() {
    @get:InputFiles
    @get:PathSensitive(PathSensitivity.NONE)
    abstract val androidStudioRuntime: ConfigurableFileCollection

    @get:OutputDirectory
    abstract val outputDir: DirectoryProperty

    @TaskAction
    fun extract() {