As title, I think the error was below. Any advise would be appreciated.

@objc func addItem(){
        let ac = UIAlertController(title: "Add Item", message: nil, preferredStyle: .alert)
        ac.addTextField { (tf) in
            tf.placeholder = "List name"
        }
        ac.addTextField { (tf) in
            tf.placeholder = "Item"
        }
        ac.addAction(UIAlertAction(title: "Create", style: .default, handler: { (action) in
            let listName = ac.textFields?[0].text ?? "Shopping"
            let name = ac.textFields?[1].text ?? "Item"

            if self.shoppingLists.isEmpty{
                let item = Item(name: name, doneStatus: false)
                let list = ShoppingList(listName: listName, items: [item])
                self.shoppingLists.insert(list, at: 0)

            }else{
                for  (i, var list) in self.shoppingLists.enumerated(){
                    if list.listName.lowercased() == listName.lowercased(){

                        self.shoppingLists.remove(at: i)

                        let item = Item(name: name, doneStatus: false)
                        list.items.append(item)
                        self.shoppingLists.insert(list, at: i)

                    }else{
                        let item = Item(name: name, doneStatus: false)
                        let list = ShoppingList(listName: listName, items: [item])
                        self.shoppingLists.insert(list, at: 0)

                    }
                }

            }

            self.tableView.reloadData()
//            let indexPath = IndexPath(row: 0, section: 0)
//            self.tableView.insertRows(at: [indexPath], with: .automatic)
        }))
        present(ac, animated: true, completion: nil)
    }