Bug report

When I use isset() on a variable variable, PHPStan reports the variable might be undefined while this is exactly what I'm trying to check.

Code snippet that reproduces the problem

https://phpstan.org/r/9140cc80-f0e1-4676-85a4-5d5b7c0e5ed4

Expected output

No error.

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This is the first issue I can report about PHPStan while we've been using it for years. Impressive!