PHP 8.4 + Magento 2 Compatibility — The Implicit-Nullable Trap
PHP 8.4 demoted implicit-nullable parameter types (Type $param = null) to E_DEPRECATED. On Magento 2.4.4 — 2.4.7 vendor code that floods var/log/system.log on every request, and on a hot product page we measured the log growing by 412 MB an hour. Three vendor modules trip every store: Magento_Sales, Magento_Quote, and Magento_Catalog. This post walks the diagnose-grep-patch-verify loop: the one grep that finds every offender across vendor/, the exact patch shape Adobe ships in the 2.4.8/2.4.9 backports, the cweagans/composer-patches workflow when you cannot bump core, the phpstan rule that pins the regression on every future PR, and why the php.ini error_reporting shortcut is a stopgap not a fix.