ios - Swift Unbalanced calls to begin/end appearance transitions for

Question

Good day, I'm new around here, hope this question isn't too silly.

I got the warning Unbalanced calls to begin/end appearance transitions for <UINavigationController: 0x7fd61043fce0> during runtime. However, I cannot find anywhere in my code that has UINavigationController, nor any other file in the project.

import UIKit
class ViewController: UIViewController,PFLogInViewControllerDelegate, PFSignUpViewControllerDelegate, FBLoginViewDelegate {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    //self.navigationController?.navigationBarHidden = true

    if(PFUser.currentUser() == nil){


        var logInViewController = PFLogInViewController()
        logInViewController.delegate = self

        //customize logInViewController
        logInViewController.fields = PFLogInFields.UsernameAndPassword | PFLogInFields.LogInButton | PFLogInFields.PasswordForgotten | PFLogInFields.Facebook | PFLogInFields.SignUpButton

        logInViewController.facebookPermissions = ["public_profile", "email", "user_friends"]

        logInViewController.logInView.logo  = UIImageView(image: UIImage(named: "Logo"))

        //create a signUpViewController instance
        var signUpViewController = PFSignUpViewController()
        signUpViewController.delegate = self

        //add signUpViewController instance to logInViewController for signUp module.
        logInViewController.signUpController = signUpViewController

        self.parentViewController?.presentViewController(logInViewController, animated: true, completion: nil)

    }else{
        FBSession.activeSession().close()
    }

}

Am I missing something that I should check?