How to fix JSON text did not start with array or object and option to allow fragments not set."

Error Domain=NSCocoaErrorDomain Code=3840 "JSON text did not start with array or object and option to allow fragments not set." UserInfo={NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}

Here is my code:

let myUrl = NSURL(string: "http://www.01coders.com/ios/userRegister.php");

let request = NSMutableURLRequest(URL : myUrl!);

request.HTTPMethod = "POST";

let postString = "username=\(username)&password=\(password)";

request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding);

let task = NSURLSession.sharedSession().dataTaskWithRequest(request){

data, response, error -> Void in

if (error != nil){

print("error=\(error)")

return

}

do{

let json = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.AllowFragments) as! NSDictionary

print("json: \(json)");

let resultValue = json["status"] as! String;

print("Result: \(resultValue)")

var isUserRegistered:Bool = false;

if(resultValue=="Success"){

isUserRegistered = true;

}

var messageTodisplay:String = json["message"] as! String;

if(!isUserRegistered){

messageTodisplay = json["message"] as! String;

}

dispatch_async(dispatch_get_main_queue(), {

let myAlert = UIAlertController(title: "Alert", message: messageTodisplay, preferredStyle: UIAlertControllerStyle.Alert);

let okaction = UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil);

myAlert.addAction(okaction);

self.presentViewController(myAlert, animated:true, completion:nil);

})

}catch let error as NSError{

print(error)

}

}

task.resume();