MySQL error when attempting to activate a fee for a product class

I may be getting this error because I've missed a step in setting up my fees; though I tried to follow the instructions on the project home page, I got the following error when I tried to activate one of the fees I'd created:

user warning: Column 'is_active' cannot be null query: INSERT INTO uc_class_fees (pcid, fid, price, is_active) VALUES ('periodic', 1, 25, NULL) in /home/hellgate/public_html/drupal/sites/all/modules/uc_fee/uc_fee.admin.inc on line 379.

(This was on the /admin/store/products/classes/[class-name]/fees page)

I changed line 377 to the following:
$is_active = ($fee['exclude'] == 1) ? (int)0 : (int)1;

And everything seemed to work....though this was a stab in the dark; there may have been a very good reason why it was trying to set $is_active to NULL instead of 1!