fillna() on CAS column not working

If I create a CAS table with missing values...

import pandas as pd
import numpy as np

df = pd.DataFrame(dict(amount=[35,40], tip=[3.5,np.nan]))

tbl = conn.upload_frame(df, casout=dict(name="test", caslib="casuser", replace=True))

...the .fillna() method does not replace the missing values:

tbl2 = tbl
tbl2['test'] = tbl2['tip].fillna(0)

tbl3 = tbl
tbl3['test'] = tbl3['tip'].fillna(0, inplace=True)

Is there any workaround? In this case, I want to add amount with tip and save the result in total_amount:

tbl['total_amount'] = tbl['amount'] + tbl['tip'].fillna(0)

Start with the fillna() behavior on the CAS column in the upload_frame example, comparing the assignment and inplace forms shown in the issue. Reproduce the missing tip value, then verify that filling it with 0 allows amount and tip to produce total_amount.