PHP 8 Upgrade Guide: Fixing Nullable Type Deprecation and Optimizing Composer Autoloading

This article addresses two common challenges faced during PHP 8+ upgrades: the `Implicitly marking parameter as nullable is deprecated` warning and conflicts between `spl_autoload_register` and Composer's autoloader. We'll dive into the root causes, provide clear code fixes, and guide you on elegantly migrating legacy autoloading logic to Composer, leading to more modern and robust PHP applications. This is an essential practical guide for developers maintaining or upgrading their projects.