Location.speed崩溃我的应用程序

Question

我正在编写一个应用程序，显示用户的纬度，经度，高度，速度，航线等。除用户的速度外，一切都显示正常。这是我的代码：

import UIKit

import CoreLocation

class ViewController: UIViewController, CLLocationManagerDelegate {

    @IBOutlet weak var latitudeLabel: UILabel!
    @IBOutlet weak var longitudeLabel: UILabel!
    @IBOutlet weak var courseLabel: UILabel!
    @IBOutlet weak var speedLabel: UILabel!
    @IBOutlet weak var altitudeLabel: UILabel!
    @IBOutlet weak var adressLabel: UILabel!

    var manager = CLLocationManager()

    override func viewDidLoad() {
        super.viewDidLoad()

        manager.delegate = self
        manager.desiredAccuracy = kCLLocationAccuracyBest
        manager.requestWhenInUseAuthorization()
        manager.startUpdatingLocation()

    }

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {

        let location = locations[0]
        self.latitudeLabel.text = String(location.coordinate.latitude)
        self.longitudeLabel.text = String(location.coordinate.longitude)
        self.courseLabel.text = String(location.course)
        self.speedLabel.text = String(location.speed)
        self.altitudeLabel.text = String(location.altitude)
        CLGeocoder().reverseGeocodeLocation(location) { (placemarks, error) in

            if error != nil {
                print(error)
            } else {
                if let placemark = placemarks?[0] {

                    var adress = ""

                    if placemark.subThoroughfare != nil {
                        adress += placemark.subThoroughfare! + " "
                    }
                    if placemark.thoroughfare != nil {
                        adress += placemark.thoroughfare! + "\n"
                    }
                    if placemark.subLocality != nil {
                        adress += placemark.subLocality! + "\n"
                    }
                    if placemark.postalCode != nil {
                        adress += placemark.postalCode! + "\n"
                    }
                    if placemark.subAdministrativeArea != nil {
                        adress += placemark.subAdministrativeArea! + "\n"
                    }
                    if placemark.country != nil {
                        adress += placemark.country! + "\n"
                    }
                    self.adressLabel.text = adress.replacingOccurrences(of: "I-280 N", with: "")
                    print(adress.replacingOccurrences(of: "I-280 N", with: ""))

                }
            }
        }
    }
}

当我运行应用程序时，使用＆＃34; self.speedLabel.text = String（location.speed）＆＃34;给我一个错误的指令错误＆＃34;致命错误：在解开一个Optional值时意外发现nil＆＃34;。我不明白为什么location.speed没有给我一个价值。然后我试了一下：

if let speed = location.speed {
    self.speedLabel.text = String(speed)
}

然后Xcode告诉我，如果没有可选值，我就不能使用if let语句。问题是，我得到的错误如果没有让我告诉我location.speed是可选的，那么为什么我不能在if中使用它。任何人都可以告诉我我的代码有什么问题，或者我可能做错了什么。谢谢。