Debugging Core Data __NSCFSet addObject nil exception

In swift 5

Create Persistence container

private final class PersistanceContainerProvider  {
    var container: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "Test")
        container.loadPersistentStores(completionHandler: { storeDescription, error in
            if let error = error as NSError? {
                fatalError("Unable to load persistance store")
            }
        })
        return container
    }()
}

Created ManagedContext with background concurrency

private init(persistentContainerProvider: DefaultPersistanceContainerProvider = PersistanceContainerProvider()){
        self.persistentContainer = persistentContainerProvider.container
        self.managedObjectContext = persistentContainer.newBackgroundContext()
        print("Wasim \(self.managedObjectContext.concurrencyType.rawValue)")
    }

Apply managedObjectContext.performAndWait

func addTargetCode(symbol: Symbol) {
        managedObjectContext.performAndWait {
        do {
            if let existing = try managedObjectContext.fetch(ManagedTargetCurrency.fetchRequest(by: symbol.code)).first {
                existing.code = symbol.code
                existing.name = symbol.name
                 try save()
            } else {
                let added = (NSEntityDescription.insertNewObject(forEntityName: ManagedTargetCurrency.entityName, into: managedObjectContext) as? ManagedTargetCurrency).require(hint: "Wrong Core Data Configuration?")
                added.code = symbol.code
                added.name = symbol.name
                 try save()
            }
        } catch let error {
            print(Errors.addError(cause: error))
        }
        }
    }

Thanks to @bteapot for suggesting I add the -com.apple.CoreData.ConcurrencyDebug 1 argument to my scheme. I got more information on how this works from Ole Begemann's excellent Core Data Concurrency Debugging article.

Adding this flag causes an exception to be thrown as soon as your code calls into your NSManagedObjectContext from an incorrect thread. This works great in Xcode, but be advised that in an Xcode Bot, this causes tests to fail with this unhelpful message:

Lost connection to test manager service