TypeError when calling Triangle.fillna() with value=None

[genedan]

Are you on the latest chainladder version?

• Yes, this bug occurs on the latest version.

Describe the bug in words

I'm currently working on this, it's a quick fix. The default value to argument value in Triangle.fillna() is None, but trying to call Triangle.fillna() without arguments leads to a TypeError.

How can the bug be reproduced?

import chainladder as cl

clrd = cl.load_sample('clrd')
clrd.fillna()

Traceback (most recent call last):
  File "/home/ubuntu/Repos/chainladder-python/.venv/lib/python3.14/site-packages/IPython/core/interactiveshell.py", line 3699, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<ipython-input-5-c623c96317f4>", line 1, in <module>
    clrd.fillna()
    ~~~~~~~~~~~^^
  File "/home/ubuntu/Repos/chainladder-python/chainladder/core/pandas.py", line 287, in fillna
    return new_obj.fillna(value=value, inplace=True)
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/Repos/chainladder-python/chainladder/core/pandas.py", line 280, in fillna
    frame = self + value * 0
                   ~~~~~~^~~
TypeError: unsupported operand type(s) for *: 'NoneType' and 'int'

What is the expected behavior?

I don't think this is something that ever worked, so removing the default argument and making it required will fix the problem without necessitating a major version change. I think we can safely classify this as a bug fix and not an API change.

It should lead to a ValueError, like it does in Pandas:

import pandas as pd
import numpy as np
df = pd.DataFrame({'a': [1, 2, 3], 'b': [4, 5, np.nan]})
df.fillna()

Traceback (most recent call last):
  File "/home/ubuntu/Repos/chainladder-python/.venv/lib/python3.14/site-packages/IPython/core/interactiveshell.py", line 3699, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<ipython-input-7-d3a028362a04>", line 1, in <module>
    df.fillna()
    ~~~~~~~~~^^
  File "/home/ubuntu/Repos/chainladder-python/.venv/lib/python3.14/site-packages/pandas/core/generic.py", line 7316, in fillna
    value, method = validate_fillna_kwargs(value, method)
                    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "/home/ubuntu/Repos/chainladder-python/.venv/lib/python3.14/site-packages/pandas/util/_validators.py", line 293, in validate_fillna_kwargs
    raise ValueError("Must specify a fill 'value' or 'method'.")
ValueError: Must specify a fill 'value' or 'method'.

There's no exception handling in this method, so it should be added.

Would you be willing to contribute this ticket?

• Yes, absolutely!
• Yes, but I would like some help.
• No.