   @available(iOS 10.0, *)
   lazy public var persistentContainer: NSPersistentContainer = {
     let container = NSPersistentContainer(name: persistentContainerName)
-    container.persistentStoreDescriptions = persistentStoreDescriptions
+    if let descriptions = persistentStoreDescriptions {
+      container.persistentStoreDescriptions = descriptions
+    }
     return container
   }()
   

    persistentContainer.loadPersistentStores(completionHandler: block)
  }
}


  
  /// Holds the configuration for the persistent store
  @available(iOS 10.0, *)
  var persistentStoreDescriptions: Array<NSPersistentStoreDescription>? {get set}
  
  /// Holds a refference to the a saving context (bg context)
  var savingContext: NSManagedObjectContext { get }
