Has anyone encountered an error where they get a nil error like this?

Runtime error
?:0: attempt to index a nil value
stack traceback:
[C]: ?
?: in function '?'
?: in function <?:215>

I'm trying to hunt down this error, but I can't seem to find the cause of it, and the stack trace doesn't help at all. Anyone have any idea how to get better debugging info?

Looks like it has to do with timer.performWithDelay when I set the number of iterations to a non-zero value the error appears. When set to 0 it doesn't appear.