在展开Optional值时意外发现nil，即使它已分配值

我正在使用 Swift 从冠状病毒 API 获取 JSON。但是，当我尝试运行代码时，出现此错误。

致命错误：在展开可选值时意外发现 nil：第 22 行

我的代码的一部分是

override func viewDidLoad() {
        super.viewDidLoad()
        
        let url = "https://api.coronavirus.data.gov.uk/v1/data?filters=areaType=nation;areaName=england&structure={%22date%22:%22date%22,%22areaName%22:%22areaName%22,%22areaCode%22:%22areaCode%22,%22newCasesByPublishDate%22:%22newCasesByPublishDate%22,%22cumCasesByPublishDate%22:%22cumCasesByPublishDate%22,%22newDeathsByDeathDate%22:%22newDeathsByDeathDate%22,%22cumDeathsByDeathDate%22:%22cumDeathsByDeathDate%22}"
        getData(from: url)
        // Do any additional setup after loading the view.
    }
    
    private func getData(from url: String) {
        
        let getfromurl = URLSession.shared.dataTask(with: URL(string: url)!, completionHandler: {data, response, error in
            guard let data = data, error == nil else{
                print("Something Went Wrong")
                return
            }
            
            //Have data
            var result: Response?
            do {
                result = try JSONDecoder().decode(Response.self, from: data)
            }
            catch{
                print("failed to convert (error.localizedDescription)")
            }
            
            guard let json = result else {
                return
            }
            
            print(json.data.date)
        })
        getfromurl.resume()
    
    }

第 22 行是：

let getfromurl = URLSession.shared.dataTask(with: URL(string: url)!, completionHandler: {data, response, error in

我很困惑，因为我认为这意味着url没有分配给它，但即使是调试器也认为它有。

更新：

我可以获取数据，但是一旦获取就会出错。错误是：

未能转换 valueNotFound(Swift.Int, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "data", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: " newDeathsByDeathDate", intValue: nil)], debugDescription: "预期的 Int 值，但发现为 null。"，underlyingError: nil))

转换失败表明在解码 JSON 和值时出错。

回答

private func getData(from url: String) {
    guard let theURL = URL(string: url) else { print ("oops"); return }
    let getfromurl = URLSession.shared.dataTask(with: theURL, completionHandler: {data, response, error in
       /* ... */
    }
}

let url = "https://api.coronavirus.data.gov.uk/v1/data?filters=areaType=nation;areaName=england&structure=%7b%22date%22:%22date%22,%22areaName%22:%22areaName%22,%22areaCode%22:%22areaCode%22,%22newCasesByPublishDate%22:%22newCasesByPublishDate%22,%22cumCasesByPublishDate%22:%22cumCasesByPublishDate%22,%22newDeathsByDeathDate%22:%22newDeathsByDeathDate%22,%22cumDeathsByDeathDate%22:%22cumDeathsByDeathDate%22%7d"

let theUrl = URL(string: url)
print (theUrl)

curl -si 'https://api.coronavirus.data.gov.uk/v1/data?filters=areaType=nation;areaName=england&structure=%7B%22name%22:%22areaName%22%7D'