Hiding Navigation Button - ios

Question

I have a simple app that allows the user to select an image from their device via Camera Roll or to take a new image. Easy.
I have two buttons;
1) on the navigation bar named Set Image which saves the image to core data
2) on the main view that opens the image picker controller.
My issue;
How do I hide the button on the navigation bar if an image has not been selected?
import UIKit
class CameraRollViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
#IBOutlet weak var imageView: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
override func viewWillAppear(_ animated: Bool) {
self.navigationController?.navigationBar.setBackgroundImage(UIImage(),for: .default)
self.navigationController?.navigationBar.shadowImage = UIImage()
self.navigationController?.navigationBar.isTranslucent = true
}
#IBAction func addImage(_ sender: Any) {
let imagePickerController = UIImagePickerController()
imagePickerController.delegate = self
let actionSheet = UIAlertController(title: "Lets customize your Reminders Page", message: "Choose a source", preferredStyle: .actionSheet)
actionSheet.addAction(UIAlertAction(title: "Camera", style: .default, handler: { (action:UIAlertAction) in
if UIImagePickerController.isSourceTypeAvailable(.camera) {
imagePickerController.sourceType = .camera
self.present(imagePickerController, animated: true, completion: nil)
}else{
print("Camera not available")
}
}))
actionSheet.addAction(UIAlertAction(title: "Photo Library", style: .default, handler: { (action:UIAlertAction) in
imagePickerController.sourceType = .photoLibrary
self.present(imagePickerController, animated: true, completion: nil)
}))
actionSheet.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
self.present(actionSheet, animated: true, completion: nil)
}
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
let image = info[UIImagePickerControllerOriginalImage] as! UIImage
imageView.image = image
picker.dismiss(animated: true, completion: nil)
}
func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
picker.dismiss(animated: true, completion: nil)
}
}
Anyone have any idea how to do this?