'Specified cast is not valid' with custom editor

[Dmitry]

Hi,
I've tried to create a custom editor for TimeSpan data field and it returns an error 'Specified cast is not valid' when I try to set value.

public class RadFilterTimeSpanEditor : RadFilterDataFieldEditor
    {
        RadMaskedTextBox _timePicker;
        public override void InitializeEditor(System.Web.UI.Control container)
        {
            _timePicker = new RadMaskedTextBox();
            _timePicker.Mask = "<0..5><0..9>:<0..5><0..9>";
            container.Controls.Add(_timePicker);
        }
        public override Type DataType
        {
            get
            {
                return typeof(TimeSpan);
            }
            set  {}
        }

        public override System.Collections.ArrayList ExtractValues()
        {
            ArrayList list = new ArrayList(1);
            if (!string.IsNullOrWhiteSpace(_timePicker.Text))
            {
                TimeSpan ts = new TimeSpan(00, int.Parse(_timePicker.Text.Substring(0, 2)), int.Parse(_timePicker.Text.Substring(2, 2)));
                list.Add(ts);
            }

            return list;
        }

        public override void SetEditorValues(System.Collections.ArrayList values)
        {
            if (values != null && values.Count > 0)
            {
                if (values[0] == null && !(values[0] is TimeSpan))
                    return;
                TimeSpan ts = (TimeSpan)values[0];
                _timePicker.Text = string.Format("{0:00}{1:00}", ts.Minutes, ts.Seconds);
            }
        }
        protected override void CopySettings(RadFilterDataFieldEditor baseEditor)
        {
            base.CopySettings(baseEditor);
            var editor = baseEditor as RadFilterTimeSpanEditor;

        }

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            RadFilterTimeSpanEditor editorTimeSpan = new RadFilterTimeSpanEditor();
            RadFilter1.FieldEditors.Add(editorTimeSpan);
            editorTimeSpan.FieldName = "ShipingDuration";
            editorTimeSpan.DisplayName = "Shipping Duration";
        }
    }
    protected void RadFilter1_FieldEditorCreating(object sender, Telerik.Web.UI.RadFilterFieldEditorCreatingEventArgs e)
    {
        if (e.EditorType == "RadFilterTimeSpanEditor")
        {
            e.Editor = new RadFilterTimeSpanEditor();
        }
    }
}

<telerik:RadFilter ID="RadFilter1" runat="server" CssClass="RadFilter RadFilter_Default RadFilter RadFilter_Default "
            FilterContainerID="RadGrid1" OnFieldEditorCreating="RadFilter1_FieldEditorCreating">
        </telerik:RadFilter>
        <telerik:RadGrid ID="RadGrid1" runat="server" AllowPaging="True" AutoGenerateColumns="False"
            CellSpacing="0" DataSourceID="ObjectDataSource1" GridLines="None">
            <ClientSettings>
                <Selecting CellSelectionMode="None"></Selecting>
            </ClientSettings>
            <MasterTableView DataSourceID="ObjectDataSource1">
                <CommandItemSettings ExportToPdfText="Export to PDF"></CommandItemSettings>
                <RowIndicatorColumn Visible="True" FilterControlAltText="Filter RowIndicator column">
                    <HeaderStyle Width="20px"></HeaderStyle>
                </RowIndicatorColumn>
                <ExpandCollapseColumn Visible="True" FilterControlAltText="Filter ExpandColumn column">
                    <HeaderStyle Width="20px"></HeaderStyle>
                </ExpandCollapseColumn>
                <Columns>
                    <telerik:GridBoundColumn DataField="OrderID" DataType="System.Int32" FilterControlAltText="Filter OrderID column"
                        HeaderText="OrderID" SortExpression="OrderID" UniqueName="OrderID">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="CustomerID" FilterControlAltText="Filter CustomerID column"
                        HeaderText="CustomerID" SortExpression="CustomerID" UniqueName="CustomerID">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="EmployeeID" DataType="System.Int32" FilterControlAltText="Filter EmployeeID column"
                        HeaderText="EmployeeID" SortExpression="EmployeeID" UniqueName="EmployeeID">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="OrderDate" DataType="System.DateTime" FilterControlAltText="Filter OrderDate column"
                        HeaderText="OrderDate" SortExpression="OrderDate" UniqueName="OrderDate">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="RequiredDate" DataType="System.DateTime" FilterControlAltText="Filter RequiredDate column"
                        HeaderText="RequiredDate" SortExpression="RequiredDate" UniqueName="RequiredDate">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShippedDate" DataType="System.DateTime" FilterControlAltText="Filter ShippedDate column"
                        HeaderText="ShippedDate" SortExpression="ShippedDate" UniqueName="ShippedDate">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipVia" DataType="System.Int32" FilterControlAltText="Filter ShipVia column"
                        HeaderText="ShipVia" SortExpression="ShipVia" UniqueName="ShipVia">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="Freight" DataType="System.Decimal" FilterControlAltText="Filter Freight column"
                        HeaderText="Freight" SortExpression="Freight" UniqueName="Freight">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipName" FilterControlAltText="Filter ShipName column"
                        HeaderText="ShipName" SortExpression="ShipName" UniqueName="ShipName">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipAddress" FilterControlAltText="Filter ShipAddress column"
                        HeaderText="ShipAddress" SortExpression="ShipAddress" UniqueName="ShipAddress">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipCity" FilterControlAltText="Filter ShipCity column"
                        HeaderText="ShipCity" SortExpression="ShipCity" UniqueName="ShipCity">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipRegion" FilterControlAltText="Filter ShipRegion column"
                        HeaderText="ShipRegion" SortExpression="ShipRegion" UniqueName="ShipRegion">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipPostalCode" FilterControlAltText="Filter ShipPostalCode column"
                        HeaderText="ShipPostalCode" SortExpression="ShipPostalCode" UniqueName="ShipPostalCode">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipCountry" FilterControlAltText="Filter ShipCountry column"
                        HeaderText="ShipCountry" SortExpression="ShipCountry" UniqueName="ShipCountry">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="ShipingDuration" DataType="System.TimeSpan" FilterControlAltText="Filter ShipingDuration column"
                        HeaderText="ShipingDuration" UniqueName="ShipingDuration" SortExpression="ShipingDuration">
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="EntityState" DataType="System.Int32" FilterControlAltText="Filter EntityState column"
                        HeaderText="EntityState" ReadOnly="True" SortExpression="EntityState" UniqueName="EntityState">
                    </telerik:GridBoundColumn>
                </Columns>
                <EditFormSettings>
                    <EditColumn FilterControlAltText="Filter EditCommandColumn column">
                    </EditColumn>
                </EditFormSettings>
            </MasterTableView>
            <FilterMenu EnableImageSprites="False">
            </FilterMenu>
        </telerik:RadGrid>
    </div>
    <asp:ObjectDataSource ID="ObjectDataSource1" runat="server" SelectMethod="GetOrders"
        TypeName="NORTHWINDModel.OrdersAdapter"></asp:ObjectDataSource>

public partial class Orders
    {
        public TimeSpan? ShipingDuration
        {
            get
            {
                return this.ShippedDate - this.OrderDate;
            }
            set { }
        }
    }