关于c#：实体的Linq不会为Left Join抛出Null引用异常

Linq to Entities NOT throwing Null reference exception for Left Join

在Linq to Object中：
访问左外部联接结果集的右表对象时，查询将引发Null引用异常。

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var customers = new Customer[]
{
new Customer{Code = 5, Name ="Sam"},
new Customer{Code = 6, Name ="Dave"},
new Customer{Code = 7, Name ="Julia"},
new Customer{Code = 8, Name ="Sue"}
};

var orders = new Order[]
{
new Order{KeyCode = 5, Product ="Book"},
//new Order{KeyCode = 6, Product ="Game"},
new Order{KeyCode = 7, Product ="Computer"},
new Order{KeyCode = 7, Product ="Mouse"},
new Order{KeyCode = 8, Product ="Shirt"},
new Order{KeyCode = 5, Product ="Underwear"}
};

var query = customers.GroupJoin(orders,
c => c.Code,
o => o.KeyCode,
(customer, order) => new { customer,order})
.SelectMany(q => q.order.DefaultIfEmpty(),(q,order)=>new{q.customer,order});

query.Where(l => l.order.Product.Contains("Book")).Dump();

像在SQLServer中一样，假设上述客户和订单数据。 Same Query(即现在与LINQ to EF)未引发空引用异常。它只是返回记录。

Why it is not throwing null reference exception ? Even Order object
for Customer{Code:6, Name:"Dave"} is null

编辑：
我尝试了一些小的变化，如下所示。

1	var result = query.Where(l => l.order.Product.Contains("Book")).ToList();

以上查询未引发Null参考异常

1	var result = query.ToList().Where(l => l.order.Product.Contains("Book"));

此查询引发异常

对具有近50,000条记录的表的两个查询均未引发异常。

在我的生产环境中，进行类似的查询，但是数量级为50,000条记录，而不是4或6条记录。在数据访问层中，我在应用所有Where过滤器后将查询结果作为List返回。没有引发异常，系统运行正常。

Do I need to Check null on Order object in Where Predicate as in
Alex Zaitsev's answer ?