Performing Multiple Actions On One Button In Xcode

Question

I keep getting the error:

Fatal error: Unexpectedly found nil while unwrapping an Optional value

when combining two actions. Not exactly sure what to do, since I have been using Xcode only for a few days now. What I would like to do is to perform several calculations/actions when the button is pressed. Thanks beforehand for the input!

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var priceTextField: UITextField!
    @IBOutlet weak var payoutTextField: UITextField!
    @IBOutlet weak var leasingTextField: UITextField!
    @IBOutlet weak var payoutLabel: UILabel!
    @IBOutlet weak var leasingsumLabel: UILabel!
    @IBOutlet weak var restsumLabel: UILabel!

    @IBAction func loanCalculate(_ sender: Any) {
        let price: Double = Double(priceTextField.text!)!
        let twentyPercentOfPrice: Double = price * 0.2
        payoutLabel.text = String(twentyPercentOfPrice)
        let leasingsum: Double = Double(leasingTextField.text!)!
        let thirtyPercentOfLeasing: Double = leasingsum * 0.3
        leasingsumLabel.text = String(thirtyPercentOfLeasing)
    }
}