Unwind segue causing fatal error - ios

Question

I keep getting fatal error:
unexpectedly found nil while unwrapping an Optional value.
I know the general sense of the error, however I don't know what I'm doing wrong to cause it.
I've narrowed the issue down to an unwind segue of mind:
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()
}
}
}
}
The issue seems to be with
#IBAction func unwindToPhotoBrowser (segue : UIStoryboardSegue) {
}
I've double checked my identifier and the connection in the story board. I have a similar project that uses a similar set up for login and that project seems to get the same error when this IBAction is removed so that's why I think it might be the issue. When I search for the action in the Find Navigator it doesn't show up with the "M" icon beside it whereas with my other project is does.