Entity for core data having nil for entityname

I am getting an error called "+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Person". The name of the entity is Person and the entity name is name which is set as a string. The whole point of this is so a user can be added with a username and this saves as core data. Any way to solve this issue? The appdelegate class is also in the code

class TableViewUsernameViewController: UIViewController {

@IBOutlet weak var tableView: UITableView!

var people: [NSManagedObject] = []

override func viewDidLoad() {
    super.viewDidLoad()
    title = "The List"
    tableView.register(UITableViewCell.self, forCellReuseIdentifier: "Cell")

    // Do any additional setup after loading the view.
}


@IBAction func addName(_ sender: Any) {
    let alert = UIAlertController(title: "New Name",
                                  message: "Add a new name",
                                  preferredStyle: .alert)

    let saveAction = UIAlertAction(title: "Save", style: .default) {
        [unowned self] action in


        guard let textField = alert.textFields?.first,
            let nameToSave = textField.text else {
                return
        }

        self.save(name: nameToSave)
        self.tableView.reloadData()
    }


    let cancelAction = UIAlertAction(title: "Cancel",
                                     style: .default)

    alert.addTextField()

    alert.addAction(saveAction)
    alert.addAction(cancelAction)

    present(alert, animated: true)
}

func save(name: String) {

    guard let appDelegate =
        UIApplication.shared.delegate as? AppDelegate else {
            return
    }

    // 1
    let managedContext =
        appDelegate.persistentContainer.viewContext

    // 2
    let entity =
        NSEntityDescription.entity(forEntityName: "Person",
                                   in: managedContext)!

    let person = NSManagedObject(entity: entity,
                                 insertInto: managedContext)

    // 3
    person.setValue(name, forKeyPath: "name")

    // 4
    do {
        try managedContext.save()
        people.append(person)
    } catch let error as NSError {
        print("Could not save. \(error), \(error.userInfo)")
    }
}

}

// MARK: - UITableViewDataSource
extension TableViewUsernameViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView,
               numberOfRowsInSection section: Int) -> Int {
    return people.count
}

func tableView(_ tableView: UITableView,
               cellForRowAt indexPath: IndexPath)
    -> UITableViewCell {

        let person = people[indexPath.row]
        let cell =
            tableView.dequeueReusableCell(withIdentifier: "Cell",
                                          for: indexPath)
        cell.textLabel?.text =
            person.value(forKeyPath: "name") as? String
        return cell
}

}

  @UIApplicationMain
  class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?


func application(_ application: UIApplication, 
didFinishLaunchingWithOptions launchOptions: 
[UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.
    return true
}

func applicationWillResignActive(_ application: UIApplication) {
    // Sent when the application is about to move from active to 
   inactive state. This can occur for certain types of temporary 
   interruptions (such as an incoming phone call or SMS message) or 
   when the user quits the application and it begins the transition to 
   the background state.
    // Use this method to pause ongoing tasks, disable timers, and 
   invalidate graphics rendering callbacks. Games should use this 
   method to pause the game.
}

func applicationDidEnterBackground(_ application: UIApplication) {
    // Use this method to release shared resources, save user data, 
invalidate timers, and store enough application state information to 
restore your application to its current state in case it is terminated 
later.
    // If your application supports background execution, this method 
is called instead of applicationWillTerminate: when the user quits.
}

func applicationWillEnterForeground(_ application: UIApplication) {
    // Called as part of the transition from the background to the 
active state; here you can undo many of the changes made on entering 
the background.
}

func applicationDidBecomeActive(_ application: UIApplication) {
    // Restart any tasks that were paused (or not yet started) while 
the application was inactive. If the application was previously in the 
background, optionally refresh the user interface.
}

func applicationWillTerminate(_ application: UIApplication) {
    // Called when the application is about to terminate. Save data if 
appropriate. See also applicationDidEnterBackground:.
    // Saves changes in the application's managed object context before 
    the application terminates.
       self.saveContext()
}

// MARK: - Core Data stack

lazy var persistentContainer: NSPersistentContainer = {
    /*
     The persistent container for the application. This implementation
     creates and returns a container, having loaded the store for the
     application to it. This property is optional since there are 
legitimate
     error conditions that could cause the creation of the store to 
fail.
     */
    let container = NSPersistentContainer(name: "QuizFinal")
    container.loadPersistentStores(completionHandler: { 
(storeDescription, error) in
        if let error = error as NSError? {
            // Replace this implementation with code to handle the 
error appropriately.
            // fatalError() causes the application to generate a crash 
log and terminate. You should not use this function in a shipping 
application, although it may be useful during development.

            /*
             Typical reasons for an error here include:
             * The parent directory does not exist, cannot be created, 
 or disallows writing.
             * The persistent store is not accessible, due to 
 permissions or data protection when the device is locked.
             * The device is out of space.
             * The store could not be migrated to the current model 
 version.
             Check the error message to determine what the actual 
 problem was.
             */
            fatalError("Unresolved error \(error), \(error.userInfo)")
        }
    })
    return container
}()

// MARK: - Core Data Saving support

func saveContext () {
    let context = persistentContainer.viewContext
    if context.hasChanges {
        do {
            try context.save()
        } catch {
            // Replace this implementation with code to handle the 
error appropriately.
            // fatalError() causes the application to generate a crash 
log and terminate. You should not use this function in a shipping 
application, although it may be useful during development.
            let nserror = error as NSError
            fatalError("Unresolved error \(nserror), \
(nserror.userInfo)")
        }
    }
}

}
//short-cut to access App Delegate
let ad = UIApplication.shared.delegate as! AppDelegate
let context = ad.persistentContainer.viewContext