private function getModuleDependencies(DependsOnModule $module)
    {
        $depends = $module->_depends();

        if (!$depends) {
            return [];
        }

        if (!is_array($depends)) {
            $message = sprintf("Method _depends of module '%s' must return an array", get_class($module));
            throw new ModuleException($module, $message);
        }

        return $depends;
    }