Added a bunch of assertions that internal assumptions are not violated (specifically, make sure args are not NULL).
Added a bunch of assertions that internal assumptions are not violated
(specifically, make sure args are not NULL).

If the expected value is not the right length, include the value found in
the error message, to make problems easier to diagnose.

PKRoma/expat,PKRoma/expat,PKRoma/expat,PKRoma/expat