Test and document our handling of nulls with getString().

Our behaviour is consistent with Crockford's.

The test confirms that the behaviour is consistent with the report
of that bug, which the submitter claims is not how it should behave.
http://code.google.com/p/android/issues/detail?id=7257

Change-Id: Ibace4bd995e3cbc8fb6c9dc509f8f4491865a647
2 files changed