BUG: 1.3.0rc Series.mode errors with BooleanDtype series containing nans

[tamargrey]

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

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

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Code Sample, a copy-pastable example

import pandas as pd

pd.Series([True, False, True, pd.NA], dtype='boolean').mode()

Problem description

The above mode call produces the following error: TypeError: int() argument must be a string, a bytes-like object or a number, not 'NAType'.

This occurs whether pd.NA or None or np.nan is used.

Expected Output

The mode call should not raise an error.

assert pd.Series([True, False, True, pd.NA], dtype='boolean').mode() is True

Output of pd.show_versions()

INSTALLED VERSIONS

commit : 2dd9e9b
python : 3.8.2.final.0
python-bits : 64
OS : Darwin
OS-release : 19.6.0
Version : Darwin Kernel Version 19.6.0: Sun Jul 5 00:43:10 PDT 2020; root:xnu-6153.141.1~9/RELEASE_X86_64
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.3.0rc1
numpy : 1.20.3
pytz : 2021.1
dateutil : 2.8.1
pip : 21.1.2
setuptools : 41.2.0
Cython : None
pytest : 6.0.1
hypothesis : None
sphinx : 3.2.1
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.11.3
IPython : 7.18.1
pandas_datareader: None
bs4 : None
bottleneck : None
fsspec : 2021.06.0
fastparquet : 0.5.0
gcsfs : None
matplotlib : 3.2.2
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 4.0.1
pyxlsb : None
s3fs : None
scipy : 1.6.3
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : 0.53.1

[simonjayhawkins]

Thanks @tamargrey for the report

The above mode call produces the following error: TypeError: int() argument must be a string, a bytes-like object or a number, not 'NAType'.

first bad commit: [b4375a4] REF: avoid unnecessary casting in algorithms (#41256) cc @jbrockmendel

Expected Output

The mode call should not raise an error.

assert pd.Series([True, False, True, pd.NA], dtype='boolean').mode() is True

The expected output is a Series, see https://pandas.pydata.org/pandas-docs/dev/reference/api/pandas.Series.mode.html

0    True
dtype: boolean

[simonjayhawkins]

Thanks @tamargrey for the report

and thanks for testing the rc!