Bug: cant upload one file only if type is list[UploadFile] | None

[euri10]

Description

I though I had the same issue as #2939 but it's slightly different, here is a test case that fails for one file and not for 2 files:

@dataclass
 class OFiles:
    file_list: Optional[List[UploadFile]]


@pytest.mark.parametrize("file_count", (1, 2))
def test_upload_multiple_ofiles_in_model(file_count: int) -> None:
    @post("/")
    async def handler(data: OFiles = Body(media_type=RequestEncodingType.MULTI_PART)) -> None:
        assert len(data.file_list) == file_count

        for file in data.file_list:
            assert await file.read() == b"1"

    with create_test_client([handler]) as client:
        files_to_upload = [("file_list", b"1") for _ in range(file_count)]
        response = client.post("/", files=files_to_upload)

        assert response.status_code == HTTP_201_CREATED

URL to code causing the issue

No response

MCVE

# Your MCVE code here

Steps to reproduce

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Screenshots

"![SCREENSHOT_DESCRIPTION](SCREENSHOT_LINK.png)"

Logs

No response

Litestar Version

2.8.2final0

Platform

• Linux
• Mac
• Windows
• Other (Please specify in the description above)

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[JacobCoffee]

May need to be a separate issue, but | None also removes the Upload File button in OpenAPI schema docs :(

from litestar import Controller, Litestar, post
from litestar.datastructures import UploadFile
from litestar.enums import RequestEncodingType
from litestar.params import Body


class Files(Controller):
    @post(path="/files/upload")
    async def upload_files(
        self,
        data: UploadFile | None = Body(media_type=RequestEncodingType.MULTI_PART),
    ) -> str:
        return data


app = Litestar(route_handlers=[Files])

Without | None

With | None

[peterschutt]

May need to be a separate issue, but | None also removes the Upload File button in OpenAPI schema docs :(

from litestar import Controller, Litestar, post
from litestar.datastructures import UploadFile
from litestar.enums import RequestEncodingType
from litestar.params import Body


class Files(Controller):
    @post(path="/files/upload")
    async def upload_files(
        self,
        data: UploadFile | None = Body(media_type=RequestEncodingType.MULTI_PART),
    ) -> str:
        return data


app = Litestar(route_handlers=[Files])

Without | None

With | None

Yeah, I think should be separate. Opened #3411.

[github-actions]

This issue has been closed in #3408. The change will be included in the upcoming patch release.

[github-actions]

A fix for this issue has been released in v2.9.0