Chapter 2 unexpectedly found nil while unwrapping an Optional value

Continuing the discussion from Errata for Core Data by Tutorials v2.2:

Whenever I run the bowtie app, I get the following message:
unexpectedly found nil while unwrapping an Optional value

The error occurs in populate() and seems to have something to do with bowtie.timesWorn!

Any clues as to what might be going on?

Again, this was my fault. Typo!