/// <summary>
 ///
 /// </summary>
 /// <param name="newItem"></param>
 /// <param name="title"></param>
 /// <param name="productList"></param>
 public Dialog(InvoiceItem newItem, string title, ProductList productList)
     : this(newItem, title, productList, 0)
 {
 }
 /// <summary>
 ///
 /// </summary>
 public Dialog(ProductList productList)
     : this(null, "Add Fields", productList)
 {
 }