Call can throw, but it is not marked with 'try' and the error is not handled Swift 4, SwiftyJSON

Question

I'm trying to get consume API REST using NSMutableURLRequest, and to parse json i'm using SwiftyJSON, Consume Rest API , my code is

func getUserLogin(username:String,password:String, onSuccess:@escaping(JSON)-> Void, onFailure: @escaping(Error)->Void){
        let url:String = baseURL+APIManager.getUserLogin
        let request: NSMutableURLRequest = NSMutableURLRequest(url: NSURL(string: url)! as URL)
        request.httpMethod="POST"
        let postString = "username="+username+"&password="+password
        request.httpBody = postString.data(using: .utf8)
        let session = URLSession.shared

        let task = session.dataTask(with: request as URLRequest,completionHandler:{data,response,error->Void in if(error != nil){onFailure(error!)

        }else {
            let result = JSON(data: data!)
            onSuccess(result)
            }

        })
        task.resume()

    }

but the xcode builder notified me thats there's error in this part

let result = JSON(data: data!)
        onSuccess(result)

any idea why? because when i try to run example project from Consume Rest API everything run normall