Change null to strict int defined preg_split limit arg function call argument
 class SomeClass
 {
     public function run()
     {
-        preg_split('/\s/', $output, NULL, PREG_SPLIT_NO_EMPTY)
+        preg_split('/\s/', $output, 0, PREG_SPLIT_NO_EMPTY)
     }
 }
                        Configure your rector.php:
<?php
use Rector\Config\RectorConfig;
use Rector\Php81\Rector\FuncCall\NullToStrictIntPregSlitFuncCallLimitArgRector;
return RectorConfig::configure()
    ->withRules([
        NullToStrictIntPregSlitFuncCallLimitArgRector::class,
    ]);