Actually, https://news.ycombinator.com/item?id=30588362 https://news.ycombinator.com/item?id=30588362 has convinced me this wouldn't necessarily solve the bug i

Actually, https://news.ycombinator.com/item?id=30588362 https://news.ycombinator.com/item?id=30588362 has convinced me this wouldn't necessarily solve the bug in question either, since it's a bug caused by (quite legitimately) re-using an existing value. Though it would be easy to implement a "free" operation by just writing `undefined`, so it would still help quite a bit, and more than suggestions like "just use an Optional/Maybe type".