private function getGroupControllerNamespace() : string
    {
        $controllerNamespace = '';

        foreach ($this->groupOptionsStack as $groupOptions) {
            if (isset($groupOptions['controllerNamespace'])) {
                // Add trailing slashes if they're not there already
                if (mb_substr($groupOptions['controllerNamespace'], -1) !== '\\') {
                    $groupOptions['controllerNamespace'] .= '\\';
                }

                $controllerNamespace .= $groupOptions['controllerNamespace'];
            }
        }

        return $controllerNamespace;
    }