private function loadCommand($class) {
        $controller = new $class();
        if (!is_a($controller, '\\mpf\\cli\\Command')) {
            $this->critical('Command `' . $class . '` must extend \\mpf\\cli\\Command!', array(
                'requestedController' => $this->request()->getController(),
                'requestedModule' => $this->request()->getModule()
            ));
            return null;
        }
        return $controller;
    }