assertThat(get(url).body.string()).isEqualTo("B")
    assertThat(server.takeRequest().headers["If-None-Match"]).isNull()
    assertThat(server.takeRequest().headers["If-None-Match"]).isEqualTo("v1")
    assertThat(server.takeRequest().headers["If-None-Match"]).isEqualTo("v1")
    assertThat(server.takeRequest().headers["If-None-Match"]).isEqualTo("v2")
  }

  @Test
  fun combinedCacheHeadersCanBeNonAscii() {

```

`Optional[str]` ব্যবহার করা মানে হল শুধু `str` নয়, এটি হতে পারে `None`-ও, যা আপনার এডিটরকে সেই ত্রুটিগুলি শনাক্ত করতে সাহায্য করবে যেখানে আপনি ধরে নিচ্ছেন যে একটি মান সবসময় `str` হবে, অথচ এটি `None`-ও হতে পারেও।

`Optional[Something]` মূলত `Union[Something, None]`-এর একটি শর্টকাট, এবং তারা সমতুল্য।

এর মানে হল, Python 3.10-এ, আপনি টাইপগুলির ইউনিয়ন ঘোষণা করতে `Something | None` ব্যবহার করতে পারেন:

//// tab | Python 3.10+

    public PagerCreator(final NamingConvention namingConvention) {
        super(namingConvention);
        setNameSuffix(SUFFIX);
        setInstanceDef(InstanceDefFactory.SESSION);
        setAutoBindingDef(AutoBindingDefFactory.NONE);
    }

    public ComponentCustomizer getPagerCustomizer() {
        return getCustomizer();
    }

    public void setPagerCustomizer(final ComponentCustomizer customizer) {
        setCustomizer(customizer);

			// Do not care If-Modified-Since, Because:
			// 1. If If-Modified-Since condition evaluates to true.
			//  If both of the If-None-Match and If-Modified-Since headers are present in the request as follows:
			// 	If-None-Match condition evaluates to false , and;
			//  If-Modified-Since condition evaluates to true ;
			// 	Then Amazon S3 returns the 304 Not Modified response code.

   * `route` is the resolved route for a connection.
   */
  internal fun isEligible(
    address: Address,
    routes: List<Route>?,
  ): Boolean {
    assertLockHeld()

    // If this connection is not accepting new exchanges, we're done.
    if (calls.size >= allocationLimit || noNewExchanges) return false

Your response model could have default values, like:

{* ../../docs_src/response_model/tutorial004_py310.py hl[9,11:12] *}

* `description: Union[str, None] = None` (or `str | None = None` in Python 3.10) has a default of `None`.
* `tax: float = 10.5` has a default of `10.5`.
* `tags: List[str] = []` has a default of an empty list: `[]`.

Seu modelo de resposta pode ter valores padrão, como:

{* ../../docs_src/response_model/tutorial004_py310.py hl[9,11:12] *}

* `description: Union[str, None] = None` (ou `str | None = None` no Python 3.10) tem um padrão de `None`.
* `tax: float = 10.5` tem um padrão de `10.5`.
* `tags: List[str] = []` tem um padrão de uma lista vazia: `[]`.

   * [WindowCounter] generally carries the client view of total and acked bytes.
   */
  fun receivingConnectionWindowChanged(windowCounter: WindowCounter)

  /** Noop implementation */
  object None : FlowControlListener {
    override fun receivingStreamWindowChanged(
      streamId: Int,
      windowCounter: WindowCounter,
      bufferSize: Long,
    ) {
    }

                return MinimalSet.of(elements);
              }
            })
        .named("MinimalSet")
        .withFeatures(
            CollectionFeature.ALLOWS_NULL_VALUES, CollectionFeature.NONE, CollectionSize.ANY)
        .createTestSuite();
  }

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: Union[bool, None] = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):