Intro to app development with Swift: Lesson 17.3 error

Hello,

i'm currently working through the book Intro to app development with Swift. At the moment i'm working on Lesson 17.3: Multiple Actions & Outlets.

I can built the app and run it in the simulator. But as soon as i want to turn on one switch i receive an error.

Unfortunately i can only find the solution for the final code of this project.

Maybe someone could help me understand & solve this error.

Error Code:

Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
2019-04-13 20:16:58.584388+0200 Color_Mix[58605:3227076] Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
(lldb)

Main.Storyboard:

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        colorView.backgroundColor = .black
    }

    @IBOutlet weak var colorView: UIView!
    
    @IBOutlet weak var redSwitch: UISwitch!
    @IBOutlet weak var greenSwitch: UISwitch!
    @IBOutlet weak var blueSwitch: UISwitch!
    
    @IBAction func switchChanged(_ sender: UISwitch) {
        updateColor()
    }
    
    func updateColor() {
        var red: CGFloat = 0
        var green: CGFloat = 0
        var blue: CGFloat = 0
        if redSwitch.isOn {
            red = 1
        }
        if greenSwitch.isOn {
            green = 1
        }
        if blueSwitch.isOn {
            blue = 1
        }
        let color = UIColor(red: red, green: green, blue: blue, alpha: 1)
        colorView.backgroundColor = color
    }
}