This is an entirely forgivable error but should have been found the first time they got an email about it:

"Oh, look, the error logs have a duplicate key exception for the primary key, how do we generate primary keys.... (facepalm)"

Funnily enough, I saw the error in their snippet as soon as I read it but dismissed it thinking there was some new-fangled python feature which allowed that to work like the function def defines that default= accepts only functions so the function gets passed? -- I haven't kept up with modern python and that sounds cool and I figured the bug couldn't be THAT simple.