`Optional[Something]` là một cách viết ngắn gọn của `Union[Something, None]`, chúng là tương đương nhau.

Điều này cũng có nghĩa là trong Python 3.10, bạn có thể sử dụng `Something | None`:

//// tab | Python 3.10+

```Python hl_lines="1"
{!> ../../docs_src/python_types/tutorial009_py310.py!}
```

from docs_src.header_params.tutorial003 import app

client = TestClient(app)


@pytest.mark.parametrize(
    "path,headers,expected_status,expected_response",
    [
        ("/items", None, 200, {"X-Token values": None}),
        ("/items", {"x-token": "foo"}, 200, {"X-Token values": ["foo"]}),
        (
            "/items",
            [("x-token", "foo"), ("x-token", "bar")],
            200,

COMMIT
* raw
-N ISTIO_OUTPUT
-N ISTIO_PRERT
-A PREROUTING -j ISTIO_PRERT
-A OUTPUT -j ISTIO_OUTPUT
-A ISTIO_OUTPUT -p udp -m mark --mark 0x539/0xfff -m udp --dport 53 -j CT --zone 1
-A ISTIO_PRERT -p udp -m mark ! --mark 0x539/0xfff -m udp --sport 53 -j CT --zone 1

	RET
TEXT ·a10(SB), 0, $0-0
	CMPL runtime·writeBarrier(SB), $0
	JEQ one
	ORQ R15, R15 // ERROR "when dynamic linking, R15 is clobbered by a global variable access and is used here"
one:
	RET
TEXT ·a11(SB), 0, $0-0
	CMPL runtime·writeBarrier(SB), $0
	JEQ one
	JMP two
one:
	ORQ R15, R15 // ERROR "when dynamic linking, R15 is clobbered by a global variable access and is used here"
two:
	RET

    assert response.status_code == 200
    assert response.json() == {
        "item_id": 5,
        "item": {"name": "Foo", "price": 3.0, "description": None, "tax": None},
    }


def test_items_6(client: TestClient):
    response = client.put(
        "/items/6",
        json={
            "item": {
                "name": "Bar",
                "price": 0.2,

    assert response.status_code == 200
    assert response.json() == {
        "item_id": 5,
        "item": {"name": "Foo", "price": 3.0, "description": None, "tax": None},
    }


@needs_py310
def test_items_6(client: TestClient):
    response = client.put(
        "/items/6",
        json={
            "item": {
                "name": "Bar",

from docs_src.header_params.tutorial003_an import app

client = TestClient(app)


@pytest.mark.parametrize(
    "path,headers,expected_status,expected_response",
    [
        ("/items", None, 200, {"X-Token values": None}),
        ("/items", {"x-token": "foo"}, 200, {"X-Token values": ["foo"]}),
        # TODO: fix this, is it a bug?

 * used. HTTP/1.x connections can carry either zero or one streams. HTTP/2 connections can carry any
 * number of streams, dynamically configured with `SETTINGS_MAX_CONCURRENT_STREAMS`. A connection
 * currently carrying zero streams is an idle stream. We keep it alive because reusing an existing
 * connection is typically faster than establishing a new one.
 *

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):

import org.apache.maven.api.services.MavenException;

@Experimental
public class ModelParserException extends MavenException {

    /**
     * The one-based index of the line containing the error.
     */
    private final int lineNumber;

    /**
     * The one-based index of the column containing the error.
     */
    private final int columnNumber;

    public ModelParserException() {
        this(null, null);