Undefined variable not detected with null coalesce operator

[mpesari]

Summary of a problem or a feature request

When using the null coalesce operator (??) phpstan seems to ignore the fact that the variable is not defined.

Code snippet that reproduces the problem

https://phpstan.org/r/8c114e31-1eb0-426b-ba2e-04a2db27759a

Expected output

Undefined variable: $world

[ondrejmirtes]

Duplicate of #1823