style: clean formatting with Ruff + Black

docs/en/docs/tutorial/query-params-str-validations.md

@@ -257,12 +257,12 @@ For example, you might try:
 q: Annotated[str | None, Query(min_length=3)] = ...
 ```
 
-But this will still expect a **string** value, and if the client omits `q` or tries to send `q=None`, FastAPI will raise a validation error.
+But this will still expect a **string** value, and if the client omits `q` or tries to send `q=None`, FastAPI will raise a **request validation error**.
 In other words, `None` is not an acceptable runtime value for query parameters — only strings are.
 
 If you want to accept special values (like `"None"` or an empty string) and interpret them as `None` in your application, you can handle them manually in your function:
 
-{* ../../docs_src/query_params_str_validations/tutorial006d_an_py310.py hl[9] *}
+{* ../../docs_src/query_params_str_validations/tutorial006d_an_py310.py hl[9,11] *}
 
 ## Query parameter list / multiple values { #query-parameter-list-multiple-values }
 

docs_src/query_params_str_validations/tutorial006d_an_py310.py

@@ -1,11 +1,19 @@
+from typing import Annotated, Optional, Union
+
 from fastapi import FastAPI, Query
-from typing import Annotated, Optional
+from pydantic import BeforeValidator
 
 app = FastAPI()
 
 
+def nullable_str(val: str) -> Union[str, None]:
+    if val in ("None", "", "null"):
+        return None
+    return val
+
+
 @app.get("/items/")
-async def read_items(q: Annotated[Optional[str], Query()] = ...):
-    if q in ("None", "", "null"):
-        q = None
+async def read_items(
+    q: Annotated[Optional[str], Query(min_length=3), BeforeValidator(nullable_str)]
+):
     return {"q": q}

tests/test_tutorial/test_query_params_str_validations/test_tutorial006d_an_py310.py

@@ -1,3 +1,4 @@
+import pytest
 from fastapi.testclient import TestClient
 
 from docs_src.query_params_str_validations.tutorial006d_an_py310 import app
@@ -5,7 +6,16 @@ from docs_src.query_params_str_validations.tutorial006d_an_py310 import app
 client = TestClient(app)
 
 
-def test_read_items():
-    response = client.get("/items/", params={"q": "None"})
+@pytest.mark.parametrize(
+    "q_value,expected",
+    [
+        ("None", None),
+        ("", None),
+        ("null", None),
+        ("hello", "hello"),
+    ],
+)
+def test_read_items(q_value, expected):
+    response = client.get("/items/", params={"q": q_value})
     assert response.status_code == 200
-    assert response.json() == {"q": None}
+    assert response.json() == {"q": expected}