PFFacebookUtils logInInBackgroundWithReadPermissions生成BFTask用户

Question

PFFacebookUtils.logInInBackgroundWithReadPermissions(["public_profile", "email"]) {
        (user: PFUser?, error: NSError?) -> Void in
        if let user = user {
            if user.isNew {
                print("User signed up and logged in through Facebook!")
            } else {
                print("User logged in through Facebook!")
            }
        } else {
            print("Uh oh. The user cancelled the Facebook login.")
        }
    }

我根据Parse的说明设置了一切。运行此代码时，user的类型为BFTask。它崩溃时出现以下错误：

-[BFTask isNew]: unrecognized selector sent to instance 0x135b05970

可能是什么问题？