Question mark displayed on UIPickerView instead of Realm data on Xcode 10

I am learning to populate a UIPickerView from Realm database.

The issue is that the UIPickerView displays "?" instead of the data.

Here is my code:

import UIKitimport RealmSwiftclass AjouterEmpruntViewController: UIViewController,    UIPickerViewDelegate, UIPickerViewDataSource {    @IBOutlet weak var PickerViewListeAmis: UIPickerView!    /* Initialisation de Realm */    let realm = try! Realm()    var data:Results<Ami>!    var listOfFriends:[Ami] = []    override func viewDidLoad() {        super.viewDidLoad()        /* Definition des sources du PickerView */        self.PickerViewListeAmis.dataSource = self        self.PickerViewListeAmis.delegate = self        /* Constitution de la liste de pseudos d'amis pour alimenter le PickerView  */        self.data = realm.objects(Ami.self)        self.listOfFriends = Array(self.data)    }    @IBAction func btnSaveEmprunt(_ sender: UIBarButtonItem) {        self.dismiss(animated: true)    }    @IBAction func btnCancelEmprunt(_ sender: UIBarButtonItem) {        self.dismiss(animated: true)    }    func numberOfComponents(in pickerView: UIPickerView) -> Int {        return 1    }    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {        return listOfFriends.count    }    private func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {        print("pseudo = "+listOfFriends[row].pseudo)        return listOfFriends[row].pseudo    }    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int)    {        print("selected Ami is "+listOfFriends[row].pseudo)    }}

I followed this tutorial http://sourcefreeze.com/ios-uipickerview-example-using-swift/

Could you please help me solve the problem?

Here is the result:Issue with ? instead of data