'Variable might not be undefined' in if-statement after in_array check.

### Bug report

In order to fix the issue, I had to define `$message = '';` before the `in_array` check.

### Code snippet that reproduces the problem

https://phpstan.org/r/2e6aa27a-398a-4bd1-8f3a-44c004dfdb46

### Expected output

No output

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