private void SaveDeletedCopies()
 {
     foreach (var itemCopy in _item.Copies.Values.ToList())
     {
         ItemCopyViewModel itemCopyViewModel;
         if (!_itemCopiesViewModel.TryGetValue(itemCopy.CopyNo, out itemCopyViewModel))   // => Deleted Copy
         {
             _item.DeleteCopy(itemCopy.CopyNo);
         }
     }
 }