protected function getConfigByTheme(array $config, $themeId = null)
    {
        if (null === $themeId) {
            $themeService = $this->getServiceLocator()->get(ThemeService::SERVICE_ID);
            $themeId = $themeService->getCurrentThemeId();
        }
        if (is_array(reset($config))) {
            if (array_key_exists($themeId, $config)) {
                $config = $config[$themeId];
            } else {
                $config = array_shift($config);
            }
        }
        return $config;
    }