[BUG] Optional multi-value option returns empty tuple instead of None

[jaklan]

Describe the bug

Optional multi-value option returns empty tuple instead of None.

To Reproduce

• Create a file main.py with:

from typing import List, Optional

import typer

app = typer.Typer()


@app.command()
def main(jobs: Optional[List[str]] = None): # or `typer.Option(None)`
    print(jobs)


if __name__ == "__main__":
    app()

• Call it with:

python main.py

• It outputs:

()

• But I expected it to output:

None

Expected behavior

The expected behavior for an empty parameter annotated with Optional and = None is both documented and commonly known - it should be just None. And that's also how it works in Typer, but for some reason - only for single-value options.

Environment

• OS: macOS
• Typer version: 0.3.2
• Python version: 3.8.5

[jaywonchung]

I encountered the same problem as well. Did you find a workaround?

[svlandeg]

Confirmed that this still seems like an issue, though the output on the current version of Typer v0.9.0 is [], not () (which is still not the expected None)

[svlandeg]

cf. also #410 for a more extensive example.

[svlandeg]

PR to fix this issue: #664