Fix Series.map default for na_action

[hamdanal]

• Tests added (Please use assert_type() to assert the type of any return value)

na_action default to None

[cmp0xff]

I tried your idea myself and found one more unaddressed case.

[hamdanal]

Looks like the overloads are not actually needed. I simplified the stub and added the tests you suggested.

[cmp0xff]

Looks like the overloads are not actually needed. I simplified the stub and added the tests you suggested.

Removing the overloads is a bit alerting. I've come up with the following examples.

>>> import pandas as pd
>>> pd.Series([1, 2, 3]).map({1: "a", 2: 1.5})
0      a
1    1.5
2    NaN
dtype: object
>>> pd.Series([1, "a"]).map({1: 1.0, "a": 2.0})
0    1.0
1    2.0
dtype: float64

The first case is pd.Series[int] becoming pd.Series[Any]. The second case is pd.Series[Any] becoming pd.Series[float]. Could you include them in the test?