展开segue会导致致命错误

Question

我一直有致命的错误：

  

在解包可选值时意外地发现了nil。

我知道错误的一般意义，但是我不知道我做错了什么导致它。

我已将问题缩小到令人放松的心态：

import UIKit
import Foundation
import CoreData
import Alamofire
import FastImageCache
import SwiftyJSON

class ViewControllerTabBar: UITabBarController {

var shouldLogin = false
var user: User? {
    didSet {
        if user != nil {
        } else {
            shouldLogin = true
        }
    }
}

var nextURLRequest: NSURLRequest?
var coreDataStack: CoreDataStack!


override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.

    UITabBar.appearance().tintColor = UIColor(red: 99/255, green: 222/255, blue: 154/255, alpha: 1)

    if let fetchRequest = coreDataStack.model.fetchRequestTemplateForName("UserFetchRequest") {

        let results = try! coreDataStack.context.executeFetchRequest(fetchRequest) as! [User]

        user = results.first
    }

}

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    if shouldLogin {
        performSegueWithIdentifier("login", sender: self)
        shouldLogin = false
    }

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@IBAction func unwindToPhotoBrowser (segue : UIStoryboardSegue) {

}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "login" && segue.destinationViewController.isKindOfClass(UINavigationController.classForCoder()) {
        let navigationController = segue.destinationViewController as! UINavigationController
        if let oauthLoginViewController = navigationController.topViewController as? OauthLoginViewController {
            oauthLoginViewController.coreDataStack = coreDataStack
        }

        if self.user != nil {
            coreDataStack.context.deleteObject(user!)
            coreDataStack.saveContext()

        }
    }
}
}

问题似乎与

有关

@IBAction func unwindToPhotoBrowser (segue : UIStoryboardSegue) {

}

我已经仔细检查了我的标识符和故事板中的连接。我有一个类似的项目，使用类似的登录设置，该项目似乎在删除此IBAction时得到相同的错误，这就是为什么我认为这可能是问题。当我在Find Navigator中搜索动作时，它并没有显示出＆＃34; M＆＃34;旁边的图标，而我的其他项目就是。