This is the correct answer. If you're curious about what other sorts of things are disallowed by common law, look at dang and tomhow's comments that say "please don't":
dang: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
tomhow: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
> This is the correct answer.
Where does that saying come from? I keep seeing it in a lot of different contexts but it somehow feels off to me in a way I can't really explain.
That answer is incorrect. Common law can only be created by courts.
Corrected second link: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...