Run analysis Install PHPStan composer require --dev phpstan/phpstan Download : phpstan_mdl78145.neon and put the file into Moodle's root folder. Run the analysis: php -dmemory_limit=1G vendor/bin/phpstan analyse --configuration phpstan_mdl78145.neon -vvv | tee result.txt Search for "Access to an undefined property". grep -i "Access to an undefined property" result.txt Verify that you only got the below result: Access to an undefined property object::$_elements.                                              Access to an undefined property object::$_elements.                                              Access to an undefined property object::$_duplicateIndex. Those errors come from PHPStan's failure to analyze the code because $_elements and $_duplicateIndex properties are already defined here and here .