AppendDataBoundItems="true"


<asp:ListItem Text="" Value=""></asp:ListItem>

<UpdateParameters>
    <asp:Parameter Name="No_Empl_Ferme" Type="Int32" ConvertEmptyStringToNull="true" />
</UpdateParameters>

protected void RequestItemFormView_ItemInserting(object sender, FormViewInsertEventArgs e)
{
    for (int i = 0; i < e.Values.Count - 1; i++)
    {
        if (e.Values[i].ToString() == string.Empty)
        {
            e.Values[i] = null;
        }
    }
}

<InsertParameters>
   <asp:Parameter Name="NullableFieldName" Type="Int32" ConvertEmptyStringToNull="true"  />
</InsertParameters>

protected void FormViewSettings_ItemUpdating(object sender, FormViewUpdateEventArgs e)
  {
     OrderedDictionary values = e.NewValues as OrderedDictionary;

     var personID = values["PersonID"];

     if (string.IsNullOrEmpty(personID.ToString()))
     {
        values.Remove("PersonID");
        values.Add("PersonID", null);
     }
  }