BUG: style.format na_rep raises error with list elements

[bluss]

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Reproducible Example

import pandas as pd

pd.DataFrame([dict(a=1, b=[1, 2, 3])]).style.format(na_rep="-").to_html()
# ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Issue Description

.style.format()'s na_rep is not compatible with non-scalar elements like lists. The problem seems to be that isna(obj) does not return a boolean in this case.

Expected Behavior

format(na_rep="-") should have the intended behaviour of styling using "-" if there is no object in the "b" column, and styling it as usual otherwise.

Note that pd.isna(pd.DataFrame([dict(a=1, b=[1, 2, 3])])) runs without error.

Installed Versions

commit           : 4bfe3d07b4858144c219b9346329027024102ab6
python           : 3.8.10.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.13.0-41-generic
Version          : #46~20.04.1-Ubuntu SMP Wed Apr 20 13:16:21 UTC 2022
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : sv_SE.UTF-8
LOCALE           : sv_SE.UTF-8

pandas           : 1.4.2
numpy            : 1.22.4
pytz             : 2022.1
dateutil         : 2.8.2
pip              : 20.0.2
setuptools       : 44.0.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 3.1.2
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
brotli           : None
fastparquet      : None
fsspec           : None
gcsfs            : None
markupsafe       : 2.1.1
matplotlib       : None
numba            : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyreadstat       : None
pyxlsb           : None
s3fs             : None
scipy            : None
snappy           : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
zstandard        : None

[attack68]

possible fix (styler_render.py 1468):

- return lambda x: na_rep if isna(x) else func_3(x)
+ return lambda x: na_rep if (isna(x) is True) else func_3(x)

[bluss]

you could say that one reason is that isna picks the array overload here but should be forced to treat it as a scalar. That would be an appropriate work saving optimization here.