Ensure ApplicationContext isn't null during initialization

[rockfordlhotka]

As business base types are instantiated, the ApplicationContext is set via the IUseApplicationContext interface.

Within the implementations of that interface, we should ensure that the provided ApplicationContext value is not null. If it is null, that leads to other bugs that are hard to debug, and it would be better to just throw an exception right away to indicate that the app environment isn't set up right, or that the business class isn't being created correctly.

[StefanOssendorf]

There should be already exceptions when trying to set the context to null.

[rockfordlhotka]

At least in CSLA 9 there certainly are cases (in the unit tests) where the context is set to null.

Maybe this has been resolved by your NRT changes in CSLA 10. My changes in v9 here throw an exception if the value is null during the IUseApplicationContext implementations.