Stub for ob_start missing null type for callback argument for 8.0 <= PHP < 8.4

[mind-bending-forks]

The stub for ob_start is missing null in the type specification for the $callback argument for 8.0 <= PHP < 8.4.

https://github.com/phpstan/php-8-stubs/blob/main/stubs/ext/standard/ob_start.php

It's not clear if the omission of null from the type specification before 8.4 was deliberate. The docs for PHP do not mention this. They also include an example whereby a null is provided as the value for the $callback argument, which appears to work fine with 8.0 <= PHP < 8.4.

https://www.php.net/manual/en/function.ob-start.php

So this appears to be a bug in the stub. It is causing PHPStan to report incorrect errors against valid code, including against the example provided in the PHP docs:

phpstan/phpstan#12282