Query parameter list / multiple values : Endpoint works but the Swagger docs not updated as expected

[UbeyOzcan]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google "How to X in FastAPI" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

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• I commit to help with one of those options 👆

Example Code

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[list[str] | None, Query()] = None):
    query_items = {"q": q}
    return query_items

Description

• Open the Browser and open the Endpoint http://localhost:8000/items/?q=foo&q=bar&q=bar&q=bar
• The expected Json output is {"q":["foo","bar","bar","bar"]}
• The actual Json output is {"q":["foo","bar","bar","bar"]}
• But, the API documentation is not updated :
  
• The expected API Documentation should looks like this :
  

Anyone has this behaviour as well with the Query parameter list / multiple values tutorial ?

Many thanks in advance !

Operating System

Windows

Operating System Details

No response

FastAPI Version

0.109.1

Pydantic Version

2.7.1

Python Version

3.12.3

Additional Context

No response

[YuriiMotov]

It's a well-known issue. Use SkipJsonSchema[None] instead of None in type annotation:

async def read_items(q: Annotated[list[str] | SkipJsonSchema[None], Query()] = None):

[UbeyOzcan]

It works perfectly thank you for the support ! :)

[NewSouthMjos]

Can we add a note to the docs about this issue? It is confusing when implementing straightforward code from the docs leads to different behavior. It took me a while to find this discussion.