There are no non-confusing options, but some of those are still clearly worse than others.

What should sorted([3, nan, 2, 4, 1]) give you in Python?

A) [1, 2, 3, 4, nan] is an good option

B) [nan, 1, 2, 3, 4] is an good option

C) An error is an good option

D) [3, nan, 1, 2, 4] is a silly, bad option. It's definitely not what you want, and it's quiet enough to slip by unnoticed. This is what you get when Nan != NaN

NaN == NaN is wrong. NaN != NaN is wrong, unintuitive, and breaks the rest of your code. If you want to signal that an operation is invalid, then throw an error. The silently nonsensical semantics of NaN are the worst possible response