线程1：致命错误：在我的viewDidLoad函数中展开Optional值时意外发现nil

Question

点击“开始游戏”后，我试图让游戏开始弹出。我已经尝试了所有内容并且我一直在获取线程1：致命错误：在第57行打开一个Optional值时意外发现nil（星号为你）  我在viewDidLoad函数中的代码。有谁知道为什么会这样？

class ViewController: UIViewController {


    var caveTunnels = CaveMaze()

    @IBOutlet var helpController: UIView!        
    @IBOutlet weak var descriptionLabel: UILabel!            
    @IBOutlet weak var caveNumber: UITextField!


    func setDescription(){
        descriptionLabel.text! = caveTunnels.description
    }


    @IBAction func helpPopover(_ sender: Any) {
        self.view.addSubview(helpController)
        helpController.center = self.view.center
    }

    @IBAction func helpClose(_ sender: Any) {
        self.helpController.removeFromSuperview()
    }


    @IBAction func moveButton(_ sender: Any) {
        let caveNum = caveNumber.text!
        guard caveNum.count > 0 else { return }
        self.descriptionLabel.text = caveTunnels.move(into: Int(caveNum)!)
    }

    @IBAction func tossButton(_ sender: Any) {
        var caveNum = caveNumber.text!
        guard caveNum.count > 0 else { return caveNum = "1" }
        self.descriptionLabel.text = caveTunnels.toss(into: Int(caveNum)!)
    }

    **override func viewDidLoad() {
        super.viewDidLoad()
        let caveTunnels = CaveMaze()
        **descriptionLabel.text = caveTunnels.description**

    }**

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}