左外部联接和带有DefaultIfEmpty的Null Ref异常

Question

我尝试使用DefaultIsEmpty进行左外部连接：

            // Get Raw Queryables
            var mainQuery = context.Query<OrderBudgetOverviewBudgetListModel>().AsQueryable();
            var openOrdersQuery = context.Query<OrderBudgetOverviewOpenOrderListModel>().AsQueryable();
            var purchasedOrdersQuery = context.Query<OrderBudgetOverviewPurchasedOrderListModel>().AsQueryable();

            // Filtering
            if (year.HasValue)
            {
                mainQuery = mainQuery.Where(x => x.BudgetYear == year.Value);
                openOrdersQuery = openOrdersQuery.Where(x => x.OrderDateYear == year.Value);
                purchasedOrdersQuery = purchasedOrdersQuery.Where(x => x.OrderDateYear == year.Value);
            }

            if (team.HasValue)
            {
                mainQuery = mainQuery.Where(x => x.Team == team.Value);
                openOrdersQuery = openOrdersQuery.Where(x => x.Team == team.Value);
                purchasedOrdersQuery = purchasedOrdersQuery.Where(x => x.Team == team.Value);
            }

            // Grouping
            var orderOpenGroupedData = openOrdersQuery
                                        .GroupBy(x => new { x.ObjectAccountNumber, Year = x.OrderDateYear, x.Team })
                                        .Select(x => new { x.Key.ObjectAccountNumber, x.Key.Year, x.Key.Team, TotalCost = x.Sum(z => z.TotalCost) });

            var orderPurchedGroupedData = purchasedOrdersQuery
                                            .GroupBy(x => new { x.ObjectAccountNumber, Year = x.OrderDateYear, x.Team })
                                            .Select(x => new { x.Key.ObjectAccountNumber, x.Key.Year, x.Key.Team, TotalCost = x.Sum(z => z.InvoiceAmount) });

            // Fill together
            var resultList = (from main in mainQuery
                              join open in orderOpenGroupedData on new { main.Team, main.ObjectAccountNumber, main.BudgetYear } equals new { open.Team, open.ObjectAccountNumber, BudgetYear = open.Year }
                              into openData
                              from open in openData.DefaultIfEmpty()
                              join purchased in orderPurchedGroupedData on new { main.Team, main.ObjectAccountNumber, main.BudgetYear } equals new { purchased.Team, purchased.ObjectAccountNumber, BudgetYear = purchased.Year }
                              into purchasedData
                              from purchased in purchasedData.DefaultIfEmpty()
                              select new { main }).ToList();

我知道“ open”和“ Purchased”可以为空-因此我会对其进行检查，但是基本上我在这里不使用它，而我仍然得到NullRefExc。

这是SQL事件探查器中的查询：

exec sp_executesql N'SELECT [x].[BudgetAmount], [x].[BudgetDescription], [x].[BudgetYear], [x].[ObjectAccountNumber], [x].[Team], [t].[ObjectAccountNumber], [t].[Year], [t].[Team], [t].[TotalCost], [t0].[ObjectAccountNumber], [t0].[Year], [t0].[Team], [t0].[TotalCost]
FROM [_INTRANET_OrderBudgetOverview_BudgetList] AS [x]
LEFT JOIN (
    SELECT [x0].[ObjectAccountNumber], [x0].[OrderDateYear] AS [Year], [x0].[Team], SUM([x0].[TotalCost]) AS [TotalCost]
    FROM [_INTRANET_OrderBudgetOverview_OpenOrderList] AS [x0]
    WHERE [x0].[OrderDateYear] = @__year_Value_1
    GROUP BY [x0].[ObjectAccountNumber], [x0].[OrderDateYear], [x0].[Team]
) AS [t] ON (([x].[Team] = [t].[Team]) AND ([x].[ObjectAccountNumber] = [t].[ObjectAccountNumber])) AND ([x].[BudgetYear] = [t].[Year])
LEFT JOIN (
    SELECT [x1].[ObjectAccountNumber], [x1].[OrderDateYear] AS [Year], [x1].[Team], SUM([x1].[InvoiceAmount]) AS [TotalCost]
    FROM [_INTRANET_OrderBudgetOverview_PurchasedOrderList] AS [x1]
    WHERE [x1].[OrderDateYear] = @__year_Value_2
    GROUP BY [x1].[ObjectAccountNumber], [x1].[OrderDateYear], [x1].[Team]
) AS [t0] ON (([x].[Team] = [t0].[Team]) AND ([x].[ObjectAccountNumber] = [t0].[ObjectAccountNumber])) AND ([x].[BudgetYear] = [t0].[Year])
WHERE [x].[BudgetYear] = @__year_Value_0',N'@__year_Value_1 int,@__year_Value_2 int,@__year_Value_0 int',@__year_Value_1=2017,@__year_Value_2=2017,@__year_Value_0=2017

这是结果：

https://imgur.com/a/SglGQ1i