var item = customers.FirstOrDefault(c => c.City == "Las Vegas");
Console.WriteLine(item == null ? "null" : item.ToString()); // vrac null

IEnumerable<Customer> emptyCustomers = Enumerable.Empty<Customer>();
item = emptyCustomers.FirstOrDefault(c => c.City == "Las Vegas");
Console.WriteLine(item == null ? "null" : item.ToString()); // vrac null
