How to Handle an index out of range error crash

Hello:

I am working with a tutorial that will help me in designing my Mac Os app.

I have the following code that is generating and error "index out of ragne" crash: on line 35.

The array is in a .plist file with 5 items in each array [0,1,2,3,4].

Lines 28 - 38 is supposed to do the following:

1. It removes all items in the pop-up button, getting rid of the Item1 and Item2 entries.
2. It adds an item for every product, showing its title.
3. It selects the first product and the first item of the pop-up button. This makes sure that everything is consistent.

Why is it generating an "index out of range" error when lines 31, 32 adds back the items to the array?

import Cocoa

class ViewController: NSViewController {
    private var overviewViewController: OverviewController?
    private var detailViewController: DetailViewController?
   
    private var products = [Product]()
    var selectedProduct: Product?
   
    @IBAction func valueChanged(_ sender: NSPopUpButton) {
       
        detailViewController?.selectedProduct = selectedProduct
        if let bookTitle = sender.selectedItem?.title,
            let index = products.firstIndex(where: {$0.title == bookTitle}) {
            selectedProduct = products[index]
        }
        overviewViewController?.selectedProduct = selectedProduct
    }
   
    @IBOutlet weak var productsButton: NSPopUpButton!
   
    override func viewDidLoad() {
        super.viewDidLoad()
       
        if let filePath = Bundle.main.path(forResource: "Products", ofType: "plist") {
            products = Product.productsList(filePath)
        }
        //1
        productsButton.removeAllItems()
        //2
        for product in products {
            productsButton.addItem(withTitle: product.title)
        }
        //3
        selectedProduct = products [0]//index out of range error
       
        productsButton.selectItem(at: 0)// Do any additional setup after loading the view.
    }
   
    override var representedObject: Any? {
        didSet {
            // Update the view, if already loaded.
        }
    }
   
    override func prepare(for segue: NSStoryboardSegue, sender: Any?) {
       
        guard let tabViewController = segue.destinationController
            as? NSTabViewController else { return }
       
        for controller in tabViewController.children {
           
            if let controller = controller as? OverviewController {
                overviewViewController = controller
                overviewViewController?.selectedProduct = selectedProduct
            }
            else if let controller = controller as? DetailViewController {
                detailViewController = controller
                detailViewController?.selectedProduct = selectedProduct
            }
        }
       
    }
   
}