C#: Lambda Update or Create object in collection

gistfile1.cs

// Extension method to interrogate a collection for a particular property and value
// If it does not exist create a new object
// return object found or created
public static T GetOrAdd<T>(this IList<T> list, Func<T, bool> predicate, Func<T> constructor)
{
    var match = list.FirstOrDefault(predicate);
    if (match == null)
    {
        match = constructor();
        list.Add(match);
    }
    
    return match;
}

// GetOrAdd Extension method implemented with Order_Attributes
public ActionResult EditVoucherEntries(string row)
{
    var rowObject = nChannel.Framework.v1_0.Utilities.JsonToXml.ConvertJsonToNameValuePair(row);
    Order_Order o = GetObject<Order_Order>(API.Get(API.Orders.Actions.orderbyid, AccountID.ToString(), rowObject["id"]));

    o.Order_Attributes.GetOrAdd(x => x.Name == "Adjustment", () => new Order_Attribute() { Name = "Adjustment" }).Value = rowObject["adj"];
    o.Order_Attributes.GetOrAdd(x => x.Name == "InvoiceDate", () => new Order_Attribute() { Name = "InvoiceDate" }).Value = rowObject["invd"];
    o.Order_Attributes.GetOrAdd(x => x.Name == "InvoiceDueDate", () => new Order_Attribute() { Name = "InvoiceDueDate" }).Value = rowObject["invdd"];
    o.Order_Attributes.GetOrAdd(x => x.Name == "InvoiceNumber", () => new Order_Attribute() { Name = "InvoiceNumber" }).Value = rowObject["invn"];

    Order_Orders orders = new Order_Orders();
    orders.Add(o);
    SendObject<Order_Orders>(API.Get(API.Orders.Actions.ordersupdate, AccountID.ToString()), APIAction.Update, orders);

    return Json(o);
}