Broken iOS 11 NavigationBar

ViewController.swift

import UIKit

class ViewController: UIViewController {
    let button = UIBarButtonItem(barButtonSystemItem: .add, target: nil, action: nil)
    override func viewDidLoad() {
        super.viewDidLoad()
        let searchBar = UISearchBar()
        searchBar.searchBarStyle = .minimal
        navigationItem.titleView = searchBar
    }
    
    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)
        if traitCollection.horizontalSizeClass == .regular {
            navigationItem.leftBarButtonItem = button
        } else {
            navigationItem.leftBarButtonItem = nil
        }
    }
}