parrot/parrot — pull request #864 by bdw (2012-11-01 16:28:20+00:00)
Title: Fix returning NULL from CallContext->get_attr

This commit checks for NULL in CallContext->get_attr,
and replaces it with PMCNULL. This fixes a crash in NQP,
which stopped me from building.

[Coke] has suggested to put this check into the (macro of) GET_ATTR,
which would save us the need to check for it everywhere, but we would
have to know it the retrieved attribute is a PMC or string or otherwise.