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iOS_Apprentice_v8.3.0 Chapter 17 Scene delegate won't save

I have an unresolved identifier at the very end of chapter 17 when I run the app. The issue is with the scene delegate save. Could you please provide direction. There is no source code published for the scene delegate file. Right at the very bottom of this list of code

import UIKit

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

var window: UIWindow?
let dataModel = DataModel()


func scene(_ scene: UIScene,
           willConnectTo session: UISceneSession,
           options connectionOptions: UIScene.ConnectionOptions) {
    let navigationController = window!.rootViewController
    as! UINavigationController
    let controller = navigationController.viewControllers[0]
    as! AllListsViewController
    controller.dataModel = dataModel
    guard let _ = (scene as? UIWindowScene) else { return }
}


func sceneDidDisconnect(_ scene: UIScene) {
  saveData()
}

func sceneDidBecomeActive(_ scene: UIScene) {
    // Called when the scene has moved from an inactive state to an active state.
    // Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
}

func sceneWillResignActive(_ scene: UIScene) {
    // Called when the scene will move from an active state to an inactive state.
    // This may occur due to temporary interruptions (ex. an incoming phone call).
}

func sceneWillEnterForeground(_ scene: UIScene) {
    // Called as the scene transitions from the background to the foreground.
    // Use this method to undo the changes made on entering the background.
}

func sceneDidEnterBackground(_ scene: UIScene) {
    saveData()
        
    }
}

// MARK:- Helper Methods
func saveData() {
dataModel.saveChecklists()
}