When I work on my own code, at home, with no-one to assist or review, I write tests, and open a PR anyway, and review it myself, sometimes the next day with fresh eyes, or even 10 minutes later after a quick walk in and out of the room and a glass of water.

If you're not confident you can review a piece of code you wrote and spot a potentially disastrous bug like the one in OP, write more tests.

Humans are very good at not spotting their own mistakes, that's why writers have editors.

These days you can dump your code/diff to ChatGPT and ask it to criticize. Often most of it is junk -- irrelevant or incorrect suggestions. But the 1 in 10 suggestions is actually useful and correct, which can be immensely helpful.