Try Rector Online | Rector - Automated Way to Instantly Upgrade and Refactor any PHP code

Run Rector on your code to see what it can do for you:

 
 final class DemoFile
 {
-    public function run(bool $param = null)
+    public function run(?bool $param = null)
     {
     }
 }

PHP snippet to change

<?php

final class DemoFile
{
    public function run(bool $param = null)
    {
    }
}

Applied Rules:

ExplicitNullableParamTypeRector

Not a change you expect?

Create an issue on GitHub
...or to speed up fix – add a test fixture

Config rector.php

<?php

use Rector\Config\RectorConfig;
use Rector\ValueObject\PhpVersion;
use Rector\Php84\Rector\Param\ExplicitNullableParamTypeRector;

return RectorConfig::configure()
    ->withPhpSets(php83: true)
    ->withPhpVersion(PhpVersion::PHP_84)
    ->withRules([
        ExplicitNullableParamTypeRector::class,    
    ]);

Rector version: 2.4.2 - released at 2026-04-16 14:00