title: Terminating app due to uncaught exception 'NSInvalidArgumentException', reason attempt to insert nil'
body: <p>I have copied the stack of coredata from new project to existing project and I am getting data from API and put it into coredata at application launch but randomly it crashes.
  Here is my log:</p>
  
  <pre><code> *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFSet addObject:]: attempt to insert nil'
  *** First throw call stack:
  (
      0   CoreFoundation                      0x000000010605a34b __exceptionPreprocess + 171
      1   libobjc.A.dylib                     0x0000000105abb21e objc_exception_throw + 48
      2   CoreFoundation                      0x00000001060c3265 +[NSException raise:format:] + 197
      3   CoreFoundation                      0x0000000105ff262b -[__NSCFSet addObject:] + 155
      4   CoreData                            0x0000000101f025bb -[NSManagedObjectContext(_NSInternalChangeProcessing) _processPendingInsertions:withDeletions:withUpdates:] + 603
      5   CoreData                            0x0000000101efcc6c -[NSManagedObjectContext(_NSInternalChangeProcessing) _processRecentChanges:] + 2348
      6   CoreData                            0x0000000101f04449 -[NSManagedObjectContext(_NSInternalChangeProcessing) _prepareForPushChanges:] + 185
      7   CoreData                            0x0000000101f00ea2 -[NSManagedObjectContext save:] + 562
      8   ETKA                                0x00000001014f73a5 _TFC4ETKA11AppDelegate11saveContextfT_T_ + 149
      9   ETKA                                0x0000000101500d71 _TFC4ETKA11AppDelegate8saveJsonfT_T_ + 6113
      10  ETKA                                0x00000001014ff459 _TFFC4ETKA11AppDelegate10parseJSON1FT_T_U_FTGSqV10Foundation4Data_GSqCSo11URLResponse_GSqPs5Error___T_ + 31257
      11  ETKA                                0x0000000101422b8b _TTRXFo_oGSqV10Foundation4Data_oGSqCSo11URLResponse_oGSqPs5Error____XFdCb_dGSqCSo6NSData_dGSqS1__dGSqCSo7NSError___ + 203
      12  CFNetwork                           0x00000001088d26b0 __75-[__NSURLSessionLocal taskForClass:request:uploadFile:bodyData:completion:]_block_invoke + 19
      13  CFNetwork                           0x00000001088d1f5c __49-[__NSCFLocalSessionTask _task_onqueue_didFinish]_block_invoke + 308
      14  Foundation                          0x00000001055bf2cd __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 7
      15  Foundation                          0x00000001055befaf -[NSBlockOperation main] + 101
      16  Foundation                          0x00000001055bd6ac -[__NSOperationInternal _start:] + 672
      17  Foundation                          0x00000001055b95ef __NSOQSchedule_f + 201
      18  libdispatch.dylib                   0x0000000106f350cd _dispatch_client_callout + 8
      19  libdispatch.dylib                   0x0000000106f12e6b _dispatch_queue_serial_drain + 236
      20  libdispatch.dylib                   0x0000000106f13b9f _dispatch_queue_invoke + 1073
      21  libdispatch.dylib                   0x0000000106f163b7 _dispatch_root_queue_drain + 720
      22  libdispatch.dylib                   0x0000000106f1608b _dispatch_worker_thread3 + 123
      23  libsystem_pthread.dylib             0x00000001072e4746 _pthread_wqthread + 1299
      24  libsystem_pthread.dylib             0x00000001072e4221 start_wqthread + 13
  )
  libc++abi.dylib: terminating with uncaught exception of type NSException
  (lldb) 
  </code></pre>
  
  <p>and here is my code in appDelegate: </p>
  
  <pre><code>import UIKit
  import GoogleMaps
  import CoreData
  
  @available(iOS 10.0, *)
  @UIApplicationMain
  class AppDelegate: UIResponder, UIApplicationDelegate {
  
      var window: UIWindow?
      var nrows = 0
      var namesArray = [String]()
      var codeArray = [String]()
      var rankingArray = [String]()
      var mornStart = [String]()
      var mornEnd = [String]()
      var eveStart = [String]()
      var eveEnd = [String]()
      var addressArray = [String]()
      var telArray = [String]()
      var latArray = [String]()
      var lngArray = [String]()
      var cityArray = [String]()
      var iDArray = [String]()
      var locss = [Locs]()
  
       func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -&gt; Bool {
  
          // Override point for customization after application launch.
           parseJSON1()
  
  
          GMSServices.provideAPIKey("AIzaSyDsDqj0EMYZ-C4lGF3tmbntZtzurLl6_J4")
  
          return true
      }
  
      func applicationWillResignActive(application: UIApplication) {
          // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
          // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
      }
  
      func applicationDidEnterBackground(application: UIApplication) {
          // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
          // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
      }
  
      func applicationWillEnterForeground(application: UIApplication) {
          // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
  
  
  
  
      }
  
      func applicationDidBecomeActive(application: UIApplication) {
          // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
      }
  
      func applicationWillTerminate(application: UIApplication) {
          // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
      }
      // MARK: - Core Data stack
  
      @available(iOS 10.0, *)
      lazy var persistentContainer: NSPersistentContainer = {
          /*
           The persistent container for the application. This implementation
           creates and returns a container, having loaded the store for the
           application to it. This property is optional since there are legitimate
           error conditions that could cause the creation of the store to fail.
           */
          let container = NSPersistentContainer(name: "Model")
          container.loadPersistentStores(completionHandler: { (storeDescription, error) in
              if let error = error as NSError? {
                  // Replace this implementation with code to handle the error appropriately.
                  // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
  
                  /*
                   Typical reasons for an error here include:
                   * The parent directory does not exist, cannot be created, or disallows writing.
                   * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                   * The device is out of space.
                   * The store could not be migrated to the current model version.
                   Check the error message to determine what the actual problem was.
                   */
                  fatalError("Unresolved error \(error), \(error.userInfo)")
              }
          })
          return container
      }()
  
      // MARK: - Core Data Saving support
  
      func saveContext () {
          let context = persistentContainer.viewContext
          if context.hasChanges {
              do {
                  try context.save()
              } catch {
                  // Replace this implementation with code to handle the error appropriately.
                  // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                  let nserror = error as NSError
                  fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
              }
          }
      }
  
  
  
      func parseJSON1(){
  
  
  
          let requestURL: NSURL = NSURL(string: "xxxxxxx")!
          let urlRequest: NSMutableURLRequest = NSMutableURLRequest(url: requestURL as URL)
          let session = URLSession.shared
          let task = session.dataTask(with: urlRequest as URLRequest) {
              (data, response, error) -&gt; Void in
  
  
              let readableJSON = JSON(data: data! , options: JSONSerialization.ReadingOptions.mutableContainers, error: nil)
  
              var Name = readableJSON[0]["Name"].stringValue as String!
              print(Name)
              self.nrows = readableJSON.count
  
              for i in 0...self.nrows{
  
                  if let Name = readableJSON[i]["Name"].string as String! {
                      var ID = readableJSON[i]["Id"].intValue
                      var iDString = String (ID)
                      self.namesArray.append(Name)
                      var code1 = readableJSON[i]["Code"].string as String!
                      if code1 == nil {
  
                          code1 = " "
                      }
                      var desc = readableJSON[i]["Address"].string as String!
                      if desc == nil {
  
                          desc = " "
                      }
                      var rank = readableJSON[i]["Ranking"].string as String!
  
                      if rank == nil {
  
                          rank = " "
                      }
                      var cit = readableJSON[i]["Province"].string as String!
                      if cit == nil {
  
                          cit = " "
                      }
                      var moS = readableJSON[i]["Morning_Start"].string as String!
  
                      if moS == nil {
  
                          moS = " "
                      }
                      var moF = readableJSON[i]["Morning_Finish"].string as String!
                      if moF == nil {
                          moF = " "
                      }
                      var evS = readableJSON[i]["Evening_Start"].string as String!
                      if evS == nil {
  
                          evS = " "
                      }
                      var evF = readableJSON[i]["Evening_Finish"].string as String!
                      if evF == nil {
  
                          evF = " "
                      }
  
                      var tel = readableJSON[i]["Telephone"].string as String!
  
                      if tel == nil {
  
                          tel = " "
                      }
                      var lat = readableJSON[i]["Lat"].double
  
  
                      let latString = String (describing: lat)
                      var lng = readableJSON[i]["Lng"].double
  
                      var lngString = String (describing: lng)
  
  
                      var newLoc = Locs(iD: iDString, state: cit!, name: Name, type: rank!, code: code1!, wHoursMorning: moS! + moF!, wHoursEvening: evS! + evF!, address: desc!, phone: tel!, lat: latString, lng: lngString)
  
                      self.locss.append(newLoc)
  
                       print(Name)
  
  
                  }
  
  
  
  
  
  
  
                  //  self.idArray.append(iDString)
  
                 // print(Name)
                  print (self.nrows)
  
  
  
              }
              /* for j in 0...self.nrows {
  
               print(self.namesArray[j])
               }*/
               self.saveJson()
  
          }
          task.resume()
          saveJson()
  
  
      }
  
      func saveJson() {
          /*   let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
           let task = Task(context: context)
           task.name = textField.text
           task.isImportant = isImp.isOn
  
           //save the data into coredata
  
           (UIApplication.shared.delegate as! AppDelegate).saveContext()*/
  
           for i in 0 ..&lt; self.locss.count{
          let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
          let store = Store(context: context)
          store.name = self.locss[i].name
          store.address = self.locss[i].address
          store.city = self.locss[i].state
          store.code = self.locss[i].code
          store.morningStart = self.locss[i].wHoursMorning
          store.eveningStart = self.locss[i].wHoursEvening
          store.telephone = self.locss[i].phone
          store.lat = self.locss[i].lat
          store.lng = self.locss[i].lng
          store.ranking = self.locss[i].type
          store.iD = self.locss[i].iD
  
      (UIApplication.shared.delegate as! AppDelegate).saveContext()
             print("savedddd")
  
  
  
          }
  
  
  
  
  
      }
  
  
  
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/dbpsK.png" rel="nofollow"><img src="https://i.stack.imgur.com/dbpsK.png" alt="here is my data model"></a></p>