public class ListOfProducts
{
    [DataMember()]
    public List<Product> ProductList { get; set; }

    public ListOfProducts()
    {
        ProductList = new List<Product>();
    }
}

public ListOfProducts GetObject()
{
    ListOfProducts Listproducts = new ListOfProducts();
    ........
    using (IDataReader reader = cmd.ExecuteReader())
    {
        while (reader.Read())
        {
            Product product = new Product(reader["Name"].ToString(), reader["Code"].ToString());
            Listproducts.ProductList.Add(product);
        }
    }
    return Listproducts;
}

void service_GetObjectCompleted(object sender, GetObjectCompletedEventArgs e)
{
    if (e.Result.Count != 0)  //throws NullReferenceException
    {
        PagedCollectionView pagingCollection = new PagedCollectionView(e.Result);
        pgrProductGrids.Source = pagingCollection;
        grdProductGrid.ItemsSource = pagingCollection;
    }
}