docs: clarify misleading 'Required, can be None' section in query param validation

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

@@ -246,11 +246,34 @@ So, when you need to declare a value as required while using `Query`, you can si
 
 ### Required, can be `None` { #required-can-be-none }
 
-You can declare that a parameter can accept `None`, but that it's still required. This would force clients to send a value, even if the value is `None`.
+You might want to declare that a parameter can accept `None`, but is still required.
 
-To do that, you can declare that `None` is a valid type but simply do not declare a default value:
+However, because of how **HTTP query parameters** work, clients cannot actually send a real `None` (or `null`) value — query parameters are always sent as **strings**.
+That means you cannot truly have a *required* parameter that also allows a real `None` value.
 
-{* ../../docs_src/query_params_str_validations/tutorial006c_an_py310.py hl[9] *}
+For example, you might try:
+
+```Python
+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.
+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:
+
+```Python
+from fastapi import FastAPI, Query
+from typing import Annotated
+
+app = FastAPI()
+
+@app.get("/items/")
+async def read_items(q: Annotated[str | None, Query()] = ...):
+    if q in ("None", "", "null"):
+        q = None
+    return {"q": q}
+```
 
 ## Query parameter list / multiple values { #query-parameter-list-multiple-values }