Executing

vendor/bin/phpstan analyze src

produces

     Internal error: Internal error: Call to a member function loadClass() on int in file           
     /home/luxemate/Projects/phpstan-rector-error/src/Rector/Rule/ImportPhpUnitFunctionsRector.php  
     Run PHPStan with -v option and post the stack trace to:                                        
     https://github.com/phpstan/phpstan/issues/new?template=Bug_report.md                           
     Child process error (exit code 1):