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。

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.

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