telerik radcombobox SelectedItem.value is returning null

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C#3.5

//the project i am working on is a dnn project and the error is related to telerik radcombobox at GetDates() the value for cboRoles.SelectedItem is null which is causing error while adding role to user


private void cboRoles_SelectedIndexChanged(object sender, EventArgs e)
{
GetDates(UserId, Int32.Parse(cboRoles.SelectedItem.Value));
BindGrid();
}