PHP New Added 9 October 2026

PHP 8.1: Passing null to parameter #1 ($string) of type string is deprecated

Built-in functions used to treat null as an empty string or zero. PHP 8.1 deprecated that, so trim(null), strlen(null) and friends now log a deprecation, and a future major version is set to make it a TypeError. The null usually comes from a missing form field, a nullable database column or a function that returns null on failure, and logs fill up after an upgrade even though nothing is broken yet.

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.

Quick fix

# How many, and where? Each line in the log gives file and line
grep -c 'Passing null to parameter' /var/log/php*.log

// Default the value where it is read
$name  = trim($_POST['name'] ?? '');
$notes = strlen((string) $row['notes']);

// Handle functions that return null on failure
$out = preg_replace('/\s+/', ' ', $input);
if ($out === null) {
    throw new RuntimeException(preg_last_error_msg());
}

# Static analysis finds the rest before production does
vendor/bin/phpstan analyse --level 8 src

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.

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.
Regenerate the autoload map with composer dump-autoload -o before investigating a class-not-found error any further.
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.
Enable full error display in development (display_errors=On, error_reporting=E_ALL). The default production settings hide the cause.
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.

wiki.php.net php.net

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