It looks like you've caused a gack.
What you are looking at is what we call a GACK. A gack is our blue screen of death, our frowny Mac icon, our “the number you have reached is no longer in service”, our “Jedediah has died of dysentery”. A gack is what happens when an error got thrown within our application and we didn’t catch it and handle it.
What this means is that it’s not your fault. It’s ours. That’s why we apologize in that message. Sorry!
This friendly message is the above-water portion of a huge iceberg of functionality. The numbers you see are part of an elaborate system for efficiently bringing these events to the attention of R&D. This post will help you understand that system, and how you can help us in getting you running safely. (Hint: steer away from icebergs.)
Despite what the above says, you can very well cause a gack- this is a great example. They're harder to debug than the average error, and can be caused by just about anything that forces an operation that should never happen.