Is that vanilla JavaScript or TypeScript? I had always thought that one of the main benefits of TS is that it would probably yell about the first case. (I currently only dabble in the JS world.)
TS only complains about valid operations if there's some potential mistake due to ambiguity, usually when relying on to strong conversions such as adding a string and an array together or some other nonsense.
It wouldn't complain about the ... usage itself because ...null is well defined and therefore not a type error.
(it would I think complain about trying to apply ... to something that isn't allowed, though I don't recall making that particular mistake yet in TS code to find out)
Though also, trivial example is trivial - I was looking for the simplest thing that was valid code and let me illustrate the general concept.