PHP 8.4: Implicitly marking parameter as nullable is deprecated

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

// Deprecated in 8.4
function f(string $name = null) {}

// Correct
function f(?string $name = null) {}

# Find every occurrence
vendor/bin/rector process src --dry-run
# or
grep -rn --include='*.php' -E '\((int|string|float|bool|array|[A-Z][A-Za-z]*) \$[a-zA-Z_]+ = null' src/

# Raise reporting during upgrades so deprecations are visible
error_reporting(E_ALL);

How to diagnose PHP errors

PHP errors are dominated by per-request resource limits (memory_limit, max_execution_time) and by autoloading. Class-not-found errors are almost never missing code. They are a namespace that does not match the PSR-4 mapping, or a stale Composer autoload map. Laravel adds a caching layer that produces genuinely confusing errors when configuration is cached with the wrong environment.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

1. Read the real limits from the running process, not from a config file: php -i | grep -E 'memory_limit|max_execution_time'. CLI and FPM have separate configurations.
2. Regenerate the autoload map with composer dump-autoload -o before investigating a class-not-found error any further.
3. For Laravel, clear cached config and routes with php artisan optimize:clear. A config cache built in the wrong environment causes errors that survive every code change.
4. Enable full error display in development (display_errors=On, error_reporting=E_ALL). The default production settings hide the cause.
5. For PDO connection refusals, test the same credentials with the database's own CLI client to separate PHP configuration from database access.

Tools worth reaching for

• php -i
• composer dump-autoload -o
• php artisan optimize:clear
• Xdebug
• tail -f storage/logs/laravel.log

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

📖 php.net

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Something missing or wrong?

This entry is maintained by hand. If the fix is out of date, incomplete, or you have a better one, email a correction and it will be reviewed.