BUG: df.reset_index(names=[None]) names index column NaN instead of None

[mvashishtha]

Pandas version checks

• I have checked that this issue has not already been reported.

• 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

import pandas as pd

df = pd.DataFrame([1])
result = df.reset_index(names=[None])
assert list(result.columns) == [None, 0], result.columns

Issue Description

reset_index(names=[None]) should add a column with name None containing the values of the index. Instead it adds a column with name np.nan.

Expected Behavior

This should be not raise an assertion:

import pandas as pd

df = pd.DataFrame([1])
result = df.reset_index(names=[None])
assert list(result.columns) == [None, 0], result.columns

Installed Versions

INSTALLED VERSIONS
------------------
commit                : fd3f57170aa1af588ba877e8e28c158a20a4886d
python                : 3.9.18.final.0
python-bits           : 64
OS                    : Darwin
OS-release            : 23.3.0
Version               : Darwin Kernel Version 23.3.0: Wed Dec 20 21:31:00 PST 2023; root:xnu-10002.81.5~7/RELEASE_ARM64_T6020
machine               : arm64
processor             : arm
byteorder             : little
LC_ALL                : None
LANG                  : en_US.UTF-8
LOCALE                : en_US.UTF-8

pandas                : 2.2.0
numpy                 : 1.26.3
pytz                  : 2023.3.post1
dateutil              : 2.8.2
setuptools            : 68.2.2
pip                   : 23.3.1
Cython                : None
pytest                : None
hypothesis            : None
sphinx                : None
blosc                 : None
feather               : None
xlsxwriter            : None
lxml.etree            : None
html5lib              : None
pymysql               : None
psycopg2              : None
jinja2                : None
IPython               : 8.18.1
pandas_datareader     : None
adbc-driver-postgresql: None
adbc-driver-sqlite    : None
bs4                   : None
bottleneck            : None
dataframe-api-compat  : None
fastparquet           : None
fsspec                : None
gcsfs                 : None
matplotlib            : None
numba                 : None
numexpr               : None
odfpy                 : None
openpyxl              : None
pandas_gbq            : None
pyarrow               : None
pyreadstat            : None
python-calamine       : None
pyxlsb                : None
s3fs                  : None
scipy                 : None
sqlalchemy            : None
tables                : None
tabulate              : None
xarray                : None
xlrd                  : None
zstandard             : None
tzdata                : 2023.4
qtpy                  : None
pyqt5                 : None

[phofl]

Hi, thanks for your report.

Inserting None into an Integer Index casts to float not to object, so this behavior is as expected