title: Why is ubiquityIdentityToken always nil?
body: <p>I am developing an iOS app that uses CloudKit. Apple's documentation says that I should use NSFileManager's ubiquityIdentityToken property to detect whether the service is available. But the property is always nil. How can I do to solve it? I am testing my app on an iPhone 5 simulator with iOS 8.2. And I have also logged into an iCloud account. I have also turned on iCloud Drive. (Someone says that turning on iCloud Drive may solve this problem, but this doesn't work for me.)</p>
  
  <p>Do I need to call NSFileManager's method URLForUbiquityContainerIdentifier:? But Apple's documentation says that it is needed for document storage. It doesn't say that it is needed for CloudKit.</p>