Optional[list] is not working with callbacks

[solesensei]

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 Typer documentation, with the integrated search.
• I already searched in Google "How to X in Typer" 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 Typer but to Click.

Commit to Help

• I commit to help with one of those options 👆

Example Code

import typer
import typing as tp

app = typer.Typer(name="abc")

def callback(
        ctx: typer.Context,
        param: typer.CallbackParam,
        value: tp.List[str] | None
) -> tp.List[str] | None:
    return value


@app.command("test", help="Test")
def test_cmd(
    abc: tp.Optional[tp.List[str]] = typer.Option(
        None, "--abc", "-a", help="abc", show_default=False,
        callback=callback,
    ),
) -> None:
    print(abc)


@app.callback()
def main():
    pass

if __name__ == "__main__":
    app()

Description

Related #410 and #664

python main.py test
site-packages/typer/main.py:637 in internal_convertor
TypeError: object of type 'NoneType' has no len()

Optional[list] = Option(None, callback=callback) not working with None's anymore.
On v0.9.0 – everything works.

Operating System

macOS

Operating System Details

No response

Typer Version

0.12.3

Python Version

Python 3.11.8

Additional Context

No response

[solesensei]

Can reproduce on 12.5 version

UPD: the fix is here #1018

[solesensei]

@tiangolo can you check?

[sfc-gh-jvasquezrojas]

I am experiencing the same issue. The problems occurs when the default value converter generate_list_convertor is executed. It does not validate if the input value is None before checking if len(value) == 0. This issue is specifically found in the following line: GitHub link.

[solesensei]

Fix is here #1018