Unexpectedly found nil

[DogandElk]

I encountered this error while attempting to use your code:

    super.viewDidLoad()

            self.username.tag = 0    Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
            self.firstname.tag = 1
            self.lastname.tag = 2

I an using xcode 13 and swift

[DogandElk]

Here is more code:

import UIKit

class ViewController: UIViewController, UITextFieldDelegate {

@IBOutlet weak var firstname: UITextField!

@IBOutlet weak var lastname: UITextField!

@IBOutlet weak var username: UITextField!

@IBOutlet weak var email: UITextField!

override func viewDidLoad() {

    super.viewDidLoad()

            self.username.tag = 0
            self.firstname.tag = 1
            self.lastname.tag = 2
            self.email.tag = 3

            self.username.delegate = self
            self.firstname.delegate = self
            self.lastname.delegate = self
            self.email.delegate = self