Series.fillna(None)

[amgcc]

Describe the bug
Series.fillna with None value fails for missing overload. It could be argued this is bad practice but it is valid according to the docs.

To Reproduce

1. Provide a minimal runnable pandas example that is not properly checked by the stubs.

import numpy as np
import pandas as pd


def main():
    ffill_limit: int = 2
    sr1 = pd.Series([0, np.nan, 5, np.nan, np.nan, np.nan, 7])
    sr2 = sr1.fillna(method="ffill", limit=ffill_limit)
    print(sr2.values)


if __name__ == '__main__':
    main()

2. Indicate which type checker you are using (mypy or pyright).
   mypy
3. Show the error message received from that type checker while checking your example.

scratch/fillna.py:7: error: No overload variant of "fillna" of "Series" matches argument types "str", "int"  [call-overload]
scratch/fillna.py:7: note: Possible overload variants:
scratch/fillna.py:7: note:     def fillna(self, value: str | bytes | date | datetime | timedelta | datetime64 | timedelta64 | bool | int | float | Timestamp | Timedelta | complex | NAType | dict[Any, Any] | Series[float] | DataFrame | None = ..., *, axis: Literal['index', 0] = ..., limit: int | None = ..., downcast: dict[Any, Any] | None = ..., inplace: Literal[True]) -> None
scratch/fillna.py:7: note:     def fillna(self, value: str | bytes | date | datetime | timedelta | datetime64 | timedelta64 | bool | int | float | Timestamp | Timedelta | complex | NAType | dict[Any, Any] | Series[float] | DataFrame | None = ..., *, axis: Literal['index', 0] = ..., limit: int | None = ..., downcast: dict[Any, Any] | None = ..., inplace: Literal[False] = ...) -> Series[float]
scratch/fillna.py:7: note:     def fillna(self, value: str | bytes | date | datetime | timedelta | datetime64 | timedelta64 | bool | int | float | Timestamp | Timedelta | complex | NAType | dict[Any, Any] | Series[float] | DataFrame | None = ..., *, axis: Literal['index', 0] = ..., inplace: bool = ..., limit: int | None = ..., downcast: dict[Any, Any] | None = ...) -> Series[float] | None

Please complete the following information:

• OS: [e.g. Windows, Linux, MacOS] Linux
• OS Version [e.g. 22] Fedora 7
• python version 3.11.8
• version of type checker 1.8.0
• version of installed pandas-stubs 2.2.0.240218

[Dr-Irv]

The issue here is that method has been deprecated since version 2.1, so it is removed from the stubs.

So this is really a docs issue, or maybe we don't want to allow None. Created pandas-dev/pandas#57723

[amgcc]

I was able to work around this in my case with Series.ffill directly. If this usage is deprecated, then there is nothing to do here. You can close this issue if you agree.

[Dr-Irv]

I was able to work around this in my case with Series.ffill directly. If this usage is deprecated, then there is nothing to do here. You can close this issue if you agree.

Yes, we will close. Discussion at pandas-dev/pandas#57723 indicates that this won't be supported in the future.