next（null）在BehaviourSubject上不起作用

Question

我有一个BehaviorSubject对象，其初始化如下：

{[s]:number}

在应用程序生命周期的整个过程中，我将其设置如下：

  if #available(iOS 13.0, *) {
    let statusBarFrame = UIView(frame: UIApplication.shared.keyWindow?.windowScene?.statusBarManager?.statusBarFrame ?? CGRect.zero)
     statusBarFrame.backgroundColor = UIColor.init(red: 243/250, green: 243/250, blue: 243/250, alpha: 1)
     UIApplication.shared.keyWindow?.addSubview(statusBarFrame)
} else {
     UIApplication.shared.statusBarView?.backgroundColor = UIColor.init(red: 243/250, green: 243/250, blue: 243/250, alpha: 1)
}

但是，当我要将其设置为null时，它将被忽略并且状态不会更新：

// Note value is an URL to an existing image 
// retrieved via an API call later on
let value = null;
navbarLogoImage = new BehaviorSubject<string>(value);

我该如何解决？