viewWillTransition runtime error in iOS app

I'm not getting the reason of below error in viewWillTransition function:--

Swift runtime failure: Unexpectedly found nil while unwrapping an Optional value + 0

 super.viewWillTransition(to: size, with: coordinator)
 view.subviews.forEach { $0.removeFromSuperview() }
 
 let deviceName = UIDevice.current.model
 if deviceName == "iPhone" {
     UserDefaults.standard.set(size.width, forKey: "RotScreenWidth")
     UserDefaults.standard.set(size.height, forKey: "RotScreenHeight")
 }
 
// var text=""
     switch UIDevice.current.orientation{
     case .portrait:
         //text="Portrait"
         self.viewDidLoad()
         case .portraitUpsideDown:
             //text="PortraitUpsideDown"
             self.viewDidLoad()
         case .landscapeLeft:
             //text="LandscapeLeft"
             self.viewDidLoad()
         case .landscapeRight:
             // text="LandscapeRight"
             self.viewDidLoad()
         default:
             //text="Another"
             self.viewDidLoad()
         }
     }

I've found this error from window -> Organiser -> crashes.

NOTE:- I've done all my design programmatically and all my design are loaded from viewDidLoad() . So I need to reload the design when there is device rotation.