CS0119 NULL异常＆amp; CS1526在foreach循环中需要一个新的表达错误

Question

我收到错误“无效操作例外”和“需要新表达”
“list”变量。任何人都可以帮助检查我的代码中的错误。

错误在foreach循环上显示null异常。为了进一步的帮助，我附上错误信息图片以便更好地理解。

        gomalEntities1 db = new gomalEntities1();

        var query = (
            from m2 in db.invoices
            join m in db.paymentDetails on m2.id equals m.inv_Id
            join m3 in db.loadings on m2.fk_loading equals m3.id
            join m4 in db.destinations on m2.fk_destination equals m4.id
            join m5 in db.vehicle_owner on m2.fk_vehicle equals m5.id
            join m6 in db.products on m2.p_Id equals m6.id
            orderby m.adv descending
            where m2.id == sesstionId select new {
                m2.tripDate,
                m2.invoiceNo,
                m6.productName,
                m4.destination1,
                m2.freight,
                m.inv_Id,
                m3.loading1,
                m2.shortage_amount,
                m2.shortage_Qty,
                m5.name,
                m5.vehicle,
                m5.mobile,
                m5.capacity,
                amount = (m.adv == true ? m.amount : 0)
            });

        var list = query.GroupBy(x => x.inv_Id).Select(y => y.FirstOrDefault());
        foreach (var r in list)
        { 
            data.Add(new reportClass {
                tripDate = r.tripDate != null ? r.tripDate.Value.ToString("D"): "",
                InvoiceNo = r.invoiceNo != null ? r.invoiceNo.ToString(): "",
                ProductNo = r.productName != null ? r.productName.ToString(): "",
                Destination = r.destination1 != null ? r.destination1.ToString(): "",
                Freight = r.freight != null ? r.freight.ToString(): "",
                Loading = r.loading1 != null ? r.loading1.ToString(): "",
                ShortAmount = r.shortage_amount != null ? r.shortage_amount.ToString(): "",
                ShortQty = r.shortage_Qty != null ? r.shortage_Qty.ToString(): "",
                TripAdvance = r.amount != null ? r.amount.ToString(): ""
            });
            totalFreight += r.freight;
            t_shortageAmount += r.shortage_amount;
            t_tripAdv += r.amount;
        }