当函数签名明确声明返回类型时，Swift期望返回空值

Question

我希望我的函数以简单字符串形式返回JSON HTTP响应。但是，当我将函数签名更改为具有'String'返回类型时，Xcode现在抱怨“ void函数中出现非预期的非空返回值” 有小费吗？在我看来，这似乎并不直观。我只想将我的JSON响应作为字符串。

    func getResponseString() -> String {
        let url = getRequestURL(origin: "test", destination: "test")!;
        // Excute HTTP Request
        let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let data = data else {
                print("Error: No data to decode")
                return "error:no data"

            }
            do {
                let responseString = String(data: data, encoding: String.Encoding.utf8)
                print("responseString = \(responseString)")
                return responseString
            } catch {
                print(error)
                return "error"
            }
        }
        task.resume()
    }