// vrac Product 1
var item = products.Single(p => p.IdProduct == 1);
Console.WriteLine(item == null ? "null" : item.ToString());

// InvalidOperationException
item = products.Single();
Console.WriteLine(item == null ? "null" : item.ToString());

// InvalidOperationException
IEnumerable<Product> emptyProducts = Enumerable.Empty<Product>();
item = emptyProducts.Single(p => p.IdProduct == 1);
Console.WriteLine(item == null ? "null" : item.ToString());
