Hi,
I just found this issue:
<?php
declare(strict_types=1);
namespace Devsense\Tests\Suppress;
/**
* @suppress PHP2436
* @suppress PHP0406
*
* Message
*/
$test = function () {
$a = null;
$b = strtoupper($a);
};

Just try to remove Message text and the error is not reported anymore.
Thank you for the fix.