在SceneDelegate.swift中做rootViewController操作后，返回按钮的响应无法返回

[XWXGitHub]

class func currentViewController() -> UIViewController {
    if let rootVC = UIApplication.shared.delegate?.window??.rootViewController {
        return self.currentViewController(from: rootVC)
    } else {
        return UIViewController()
    }
}

在控制台打印了下结果如下

if let rootVC = UIApplication.shared.delegate?.window??.rootViewController
p  rootVC
(UIViewController?) $R0 = nil