I've been working on a ticket at work for a few weeks (took so long because of hospital stays and sickness), but couldn't find a solution. Finally, yesterday I wrote a fix. The previous guy removed some elements of the list without notifying the framework, so to speak, and that resulted in the error. I've been looking at all places, but that one. Hopefully the tester will give a green light for production, as this will fix another ticket as well.