Code actuel :

private function get_request_handler(): ?RequestHandler
{
$action = $this->request->get('action') ?: $this->request->get('ac_action');
return $this->request_handlers[$action] ?? null;
}

Erreur

Deprecated: Using null as an array offset is deprecated, use an empty string instead in /Users/xxxx/zzzzz/xxxx/app/public/qqq/plugins/admin-columns-pro/admin-columns/classes/RequestHandlerFactory.php on line 38

Correctif:

private function get_request_handler(): ?RequestHandler
{
$action = $this->request->get('action') ?: $this->request->get('ac_action');
if (!is_string($action) || $action === '') {return null;}
if (!is_array($this->request_handlers)) {return null;}
$handler = $this->request_handlers[$action] ?? null;
return $handler instanceof RequestHandler ? $handler : null;
}