I really enjoy these posts. Thank you for taking the time to do this work. An understandable refactoring error, but in the problem code you only save if the file doesn't exist, but in the refactored code you left in the negation, meaning if the file doesn't exist you raise a File Exists exception. I'll delete myself if I've read that wrong :).

There's a waiting list get access to the Codex Sandbox. You should mention that before having people sign up for something. This site requires phone numbers, and even more info to get on the wait list. I also don't see an obvious way to delete the account .

Isn't there a boolean-to-int conversion and that will result in a valid domain object of 0 (zero)? Maybe C handles this better than Javascript does.

I wrote this same thing on Reddit recently and was downvoted to hell! I feel validated reading this.