Issue Description: I'm having problems with signing in and sign up iOS sdk. I setup parse server on heroku, tested it with: let testObject = PFObject(className: "TestObject") testObject["foo"] = "bar" testObject.saveInBackgroundWithBlock { (success: Bool, error: NSError?) -> Void in print("Object has been saved.") } and the object saved successfully to mLab. Then when I tried to sign a user up or log a user in. I got an error: schema mismatch for _Session.user; expected Pointer but got String There was an issue already posted but it was closed and was for the js SDK. how would one solve this for iOS sdk?