BUG: .replace does not support None as a target value

[jmg-duarte]

Pandas version checks

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• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

pd.DataFrame({'a': [pd.NA]}).replace(pd.NA, None)

Issue Description

The replace function uses None instead of a sentinel value to check for a missing argument, thus it does not allow None to be used.

The fillna function also has this problem.

Expected Behavior

The replace function should allow the usage of None as a target value.

Installed Versions

INSTALLED VERSIONS

commit : 66e3805
python : 3.8.10.final.0
python-bits : 64
OS : Darwin
OS-release : 20.6.0
Version : Darwin Kernel Version 20.6.0: Wed Jun 23 00:26:31 PDT 2021; root:xnu-7195.141.2~5/RELEASE_X86_64
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_GB.UTF-8
LOCALE : en_GB.UTF-8

pandas : 1.3.5
numpy : 1.18.5
pytz : 2021.3
dateutil : 2.8.2
pip : 21.3.1
setuptools : 59.8.0
Cython : 0.29.26
pytest : 6.2.5
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : 1.1
pymysql : None
psycopg2 : None
jinja2 : None
IPython : None
pandas_datareader: None
bs4 : None
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyxlsb : None
s3fs : None
scipy : 1.7.3
sqlalchemy : 1.4.30
tables : None
tabulate : None
xarray : 0.20.2
xlrd : None
xlwt : None
numba : 0.49.1

[jreback]

this is changed in 1.4.0rc0
pls check

[jmg-duarte]

It works for .replace but not for .fillna should I rename the issue instead of opening a new one?

Any idea when 1.4.0 will be released?

[jreback]

shortly