Rule source on GitHub

DowngradeArrayMergeCallWithoutArgumentsRector

Add missing param to array_merge and array_merge_recursive

 class SomeClass
 {
     public function run()
     {
-        array_merge();
-        array_merge_recursive();
+        array_merge([]);
+        array_merge_recursive([]);
     }
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp74\Rector\FuncCall\DowngradeArrayMergeCallWithoutArgumentsRector;

return RectorConfig::configure()
    ->withRules([
        DowngradeArrayMergeCallWithoutArgumentsRector::class,
    ]);