The first complaint looks valid but really poorly addressed by the digital overlord - I don't know the codebase but in general this is something that human review may have flagged up too. I saw your comment "this never happens", but that makes it all the more important to fix the code.

Think of it this way: if a field is never undefined because it is always set on every possible code path, then you shouldn't put a default but instead do error handling (and logging!) when encountering undefined. Assigning a default value on a case that should not exist is a problem because if for any reason (in the future) it does exist, it shouldn't just gracefully apply your assumption. Assigning a default value is what leads to hidden tech debt in this case, because it will mask future errors.