BUG: .round causes TypeError / NaN-

[SSchleehauf]

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

df = pd.DataFrame([{'start': pd.Timestamp('2025-01-01 10:00:00'), 'end':pd.Timestamp('2025-01-01 10:00:15.12345678')},
                   {'start': pd.Timestamp('2025-01-01 10:00:30.999999'), 'end':pd.Timestamp('2025-01-01 10:00:45')}])
df['pause_duration'] = (df['start'].shift(-1) - df['end']).apply(lambda x: pd.NA if pd.isna(x) else x.total_seconds())
df['pause_duration'].round(1)

Issue Description

In pandas 2.2.3 rounding of Nan values just silently failed (values did not get rounded) while the same code causes a TypeError in 2.3.0

Sample data preparation:

import pandas as pd
df = pd.DataFrame([{'start': pd.Timestamp('2025-01-01 10:00:00'), 'end':pd.Timestamp('2025-01-01 10:00:15.12345678')},
                   {'start': pd.Timestamp('2025-01-01 10:00:30.999999'), 'end':pd.Timestamp('2025-01-01 10:00:45')}])
df['pause_duration'] = (df['start'].shift(-1) - df['end']).apply(lambda x: pd.NA if pd.isna(x) else x.total_seconds())
df['pause_duration']
Version: 2.2.3
Out[4]: 
0    15.876542
1         <NA>
Name: pause_duration, dtype: object```

Round fails for 2.2.3:
```python
df['pause_duration'].round(1)
Out[5]: 
0    15.876542
1         <NA>

In 2.3.0 this causes a TypeError instead:

import pandas as pd
print('Version:', pd.__version__)
df = pd.DataFrame([{'start': pd.Timestamp('2025-01-01 10:00:00'), 'end':pd.Timestamp('2025-01-01 10:00:15.12345678')},
                   {'start': pd.Timestamp('2025-01-01 10:00:30.999999'), 'end':pd.Timestamp('2025-01-01 10:00:45')}])
df['pause_duration'] = (df['start'].shift(-1) - df['end']).apply(lambda x: pd.NA if pd.isna(x) else x.total_seconds())
df['pause_duration']
Version: 2.3.0
Out[14]: 
0    15.876542
1         <NA>
Name: pause_duration, dtype: object

Round causes a TypeError:

>>> df['pause_duration'].round(1)
Traceback (most recent call last):
  File "C:\Users\Schleehauf\PycharmProjects\viodata\viotools\.venv\Lib\site-packages\IPython\core\interactiveshell.py", line 3672, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-15-0e359609e34a>", line 1, in <module>
    df['pause_duration'].round(1)
  File "C:\Users\Schleehauf\PycharmProjects\viodata\viotools\.venv\Lib\site-packages\pandas\core\series.py", line 2818, in round
TypeError: Expected numeric dtype, got object instead.

For both versions, type conversion (and rounding) only works with pyarrow:

df['pause_duration'].astype('float[pyarrow]').round(1)
Out[20]: 
0    15.9
1    <NA>
Name: pause_duration, dtype: float[pyarrow]

And fails with TypeError:

df['pause_duration'].astype(float).round(1)
Traceback (most recent call last):
...
TypeError: float() argument must be a string or a real number, not 'NAType'

Expected Behavior

1. Do not throw an exception but warn instead
2. When subtracting Timestamps the datatype shoulde be timedelta and not object even when there are NaT values
3. an timedelta-NaN that has a total_seconds()-method returning float-nan such that

df['pause_duration'].apply(lambda x: x.total_seconds())
Traceback (most recent call last):
...
AttributeError: 'float' object has no attribute 'total_seconds'

will just work in the future and yields the same result as df['pause_duration'].astype('float[pyarrow]').round(1)

Installed Versions

pd.show_versions()
INSTALLED VERSIONS

commit : 2cc3762
python : 3.12.10
python-bits : 64
OS : Windows
OS-release : 11
Version : 10.0.26100
machine : AMD64
processor : Intel64 Family 6 Model 186 Stepping 2, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : de_DE.cp1252
pandas : 2.3.0
numpy : 2.2.6
pytz : 2025.2
dateutil : 2.9.0.post0
pip : None
Cython : None
sphinx : None
IPython : 9.3.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.13.4
blosc : None
bottleneck : 1.5.0
dataframe-api-compat : None
fastparquet : None
fsspec : 2025.5.1
html5lib : None
hypothesis : None
gcsfs : None
jinja2 : 3.1.6
lxml.etree : 5.4.0
matplotlib : 3.10.3
numba : 0.61.2
numexpr : 2.11.0
odfpy : None
openpyxl : 3.1.5
pandas_gbq : None
psycopg2 : None
pymysql : None
pyarrow : 20.0.0
pyreadstat : None
pytest : 8.4.1
python-calamine : None
pyxlsb : 1.0.10
s3fs : 2025.5.1
scipy : None
sqlalchemy : None
tables : None
tabulate : 0.9.0
xarray : None
xlrd : 2.0.2
xlsxwriter : 3.2.5
zstandard : 0.23.0
tzdata : 2025.2
qtpy : None
pyqt5 : None