Bug report

If an array has been documented with an optional key, and then a null coalesce assignment is used to make sure the key exists, PHPStan doesn't realise that the key always exists in the array after the assignment.

Code snippet that reproduces the problem

https://phpstan.org/r/91be56c3-ab29-44e8-a2d3-059d3a7f9652

Expected output

No errors