Run analysis Install PHPStan composer require --dev phpstan/phpstan Download : phpstan_mdl78163.neon and put the file into Moodle's root folder. Run the analysis: php -dmemory_limit=1G vendor/bin/phpstan analyse --configuration phpstan_mdl78163.neon -vvv | tee result.txt Search for "Access to an undefined property". grep -i "Access to an undefined property" result.txt Verify that you will have a bunch of undefined property errors. That was a false alarm because all properties have been defined in the parent class. For example: MoodleQuickForm_text::$_flagFrozen The $_flagFrozen has been defined in the parent class HTML_QuickForm_element.