For example , you may get a NullReferenceException on a line that calls the internal design-time assemblies , which you can 't debug , so you 're left wondering which service failed where .
例如，您可能在调用内部设计时程序集的行中得到NullReferenceException，而您无法调试该错误，因此您只能纳闷哪个服务在哪个地方失败了。
nullreferenceexception