DataBound control's UpdateMethod returns error ASP.NET WebForms 4.5

[gregory]

I'm experimenting with ASP.NET new modelbinding and faced a little problem: SelectMethod works just fine and update method gets called without parameter or says that parameter must be nullable, because its null.\[code\]<asp:FormView ID="fv" runat="server" SelectMethod="GetProduct" ItemType="CM.Product" UpdateMethod="UpdateProduct" RenderOuterTable="False" DataKeyNames="ID" DefaultMode="Edit"> <EditItemTemplate> <asp:HiddenField runat="server" Value="http://stackoverflow.com/questions/12744255/<%# Item.ID %>" ID="idField"/> <h1>Product Details</h1> <br> <asp:LinkButton runat="server" ID="btnSave" Text="Save" ClientIDMode="Static" CommandName="Update" /> </div> <table class="tableview"> <tr> <td>Name </td> <td> <asp:TextBox runat="server" ID="txtName" MaxLength="100" Text='<%# Item.Name %>'></asp:TextBox> </td>...........\[/code\]and in codebehind: \[code\] public void UpdateProduct(long prod) { } \[/code\]Product:\[code\] public class Product { #region Properties public long ID { get; set; } public string Name { get; set; }....\[/code\]When it comes to \[code\]UpdateProduct\[/code\] error appears: \[quote\] A null value for parameter 'prod' of non-nullable type 'System.Int64' for method 'Void UpdateProduct(Int64)' in 'administration_CM_ProductDetails'. An optional parameter must be a reference type or a nullable type.\[/quote\]What can cause that?