linq 升序排序 空值放后面并根据另一个字段进行多重排序

 List<PickingInfo> res = GetDatas();
            var _d = (from e in res
                      select new
                      {
                          aa = e.pickingLibraryName == "" || e.pickingLibraryName == null ? -1 : 0,
                          e
                      }).OrderBy(c => c.e.pickingLibraryName).OrderByDescending(h => h.aa).OrderBy(c => c.e.CommodityBarCode).Select(h => h.e).ToList();//.ToDataTable();
            return JsonConvert.SerializeObject(_d);