title: When I go back to menu, the App crashes (Thread 1: signal SIGABRT)
body: <p>I am almost finished with my App "AR Note".
  There is only one bug I need to fix.</p>
  
  <p>I have a main menu with 7 buttons linking to view controllers. To go back to main menu I use </p>
  
  <pre><code>@IBAction func unwindFromSources(segue: UIStoryboardSegue){
      }
  </code></pre>
  
  <p>In my old version this works perfectly fine. All I changed is, that the background of my main menu is a blurred camera view, which works pretty good. Now, with this blur-camera-view-background, the App always crashes with Thread 1: signal SIGABRT! This seems to me awkward because it says no errors, and without the blurred camera view background the back-buttons are working fine. </p>
  
  <p>Here is my main menu code:</p>
  
  <pre><code>import UIKit
  import AVFoundation
  
  class ViewControllerBlurrHome: UIViewController {
  
      @IBAction func unwindFromSources(segue: UIStoryboardSegue){
      }
  
      let session: AVCaptureSession = AVCaptureSession()
  
      override func viewDidLoad() {
          super.viewDidLoad()
      }
  
  
  
      override func viewWillAppear(_ animated: Bool) {
          super.viewWillAppear(animated)
  
          session.sessionPreset = AVCaptureSession.Preset.high
  
          if let device = AVCaptureDevice.default(for: AVMediaType.video) {
              do {
                  try session.addInput(AVCaptureDeviceInput(device: device))
  
              } catch {
                  print(error.localizedDescription)
              }
  
              let previewLayer = AVCaptureVideoPreviewLayer(session: session)
  
              self.view.layer.insertSublayer(previewLayer,at:0)
              previewLayer.frame = self.view.layer.bounds
  
          }
  
  
  
          session.startRunning()
  
          let blur = UIBlurEffect(style: .regular)
          let blurView = UIVisualEffectView(effect: blur)
          blurView.frame = self.view.bounds
          blurView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
          self.view.insertSubview(blurView,at:1)
  
      }
  
  
  // ShareButton
      @IBAction func sharePressed(_ sender: Any) {
          let activityVC = UIActivityViewController(activityItems: ["enter App Link here"], applicationActivities: nil)
          activityVC.popoverPresentationController?.sourceView = self.view
          self.present(activityVC, animated: true, completion: nil)
      }
  
  
  }
  </code></pre>
  
  <p>This is how my main menu looks like:</p>
  
  <p><img src="https://i.stack.imgur.com/CvrVm.png" alt="image1"></p>
  
  <p>This is how my main.storyboard looks like:</p>
  
  <p><img src="https://i.stack.imgur.com/7ISvX.png" alt="image2"></p>
  
  <p>This is how I use the back-buttons:</p>
  
  <p><img src="https://i.stack.imgur.com/ckYs5.png" alt="image3"></p>
  
  <p>This is an alternative <code>viewcontroller.swift</code>, without the blur stuff, which works perfectly fine:</p>
  
  <pre><code>import UIKit
  
  class ViewControllerBasis: UIViewController {
  
  
      @IBAction func unwindFromSources(segue: UIStoryboardSegue){
      }
  
  
      override func viewDidLoad() {
          super.viewDidLoad()
  
          // Do any additional setup after loading the view.
      }
  
      override func didReceiveMemoryWarning() {
          super.didReceiveMemoryWarning()
          // Dispose of any resources that can be recreated.
      }
  
  
  
      @IBAction func sharePressed(_ sender: Any) {
          let activityVC = UIActivityViewController(activityItems: ["enter App Link here"], applicationActivities: nil)
          activityVC.popoverPresentationController?.sourceView = self.view
          self.present(activityVC, animated: true, completion: nil)
      }
  </code></pre>
  
  <p>DO you mean this?</p>
  
  <p><a href="https://i.stack.imgur.com/JANiJ.png" rel="nofollow noreferrer">image4</a></p>
  
  <p>There is this:</p>
  
  <p><a href="https://i.stack.imgur.com/IOzR7.png" rel="nofollow noreferrer">image5</a></p>
  
  <p>and this:</p>
  
  <p><a href="https://i.stack.imgur.com/f9laS.png" rel="nofollow noreferrer">image6</a></p>