Bug report

I'm getting Offset 'another'\|'some' does not exist on array(?'some' => string, ?'another' => string). When I try run in a function that receive the key as function argument and validate if the argument value is strict to some and another.

Code snippet that reproduces the problem

https://phpstan.org/r/dd639e0b-0c5d-45f1-a22e-7727f04cf471

Expected output

No errors!