问由于导致的运行时错误

EN

public class ServiceCalls : NSManagedObject {
  /*
             class func getContext () -> NSManagedObjectContext {
        let appDelegate = UIApplication.shared.delegate as! AppDelegate

        let moc = NSManagedObjectContext(concurrencyType:.mainQueueConcurrencyType)
        let privateMOC = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
        privateMOC.parent = moc

        privateMOC.perform({
            do {
                try privateMOC.save()
            } catch {
                fatalError("Failure to save context: \(error)")
            }
        })
        return appDelegate.persistentContainer.viewContext
    }
             */ // tried this but didn't work

     class func getContext () -> NSManagedObjectContext {
        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        return appDelegate.persistentContainer.viewContext
    }

class func SaveCustomerContacts(name : String,id : String){

let context = getContext()
let entity =  NSEntityDescription.entity(forEntityName: "AllCustomerContacts_Tbl", in: context)
let newDoc = NSManagedObject(entity: entity!, insertInto: context)

newDoc.setValue(name, forKey: "contactName")
newDoc.setValue(id, forKey: "id") 



    //save the object
do {
    try context.save()
    print("saved Customer contacts in Database yayy!")

} catch let error as NSError  {
    print("Could not save \(error), \(error.userInfo)")
} catch {
    let nserror = error as NSError
    fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}

    [error] error: Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.  -[__NSCFSet addObject:]: attempt to insert nil with userInfo (null)
CoreData: error: Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.  -[__NSCFSet addObject:]: attempt to insert nil with userInfo (null)
2017-07-31 16:09:20.908 Sales CRM[5846:202190] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFSet addObject:]: attempt to insert nil'
*** First throw call stack: