I had occasion to pass some null values to Test::More's is() multisub, and got an unexpected fault - NULL pmc access, etc.
Bacek mentioned in the commit comments to cs#  that discussion was needed on how Test::More handles null, so I have created this ticket to host that discussion.
To get started, I am committing a patch (cs# ) that adds is_null as a test assertion, as well as adding support for null values to the various is() multisub elements.
I think that "null happens", which is especially vexing when calling from NQP to PIR. So I think that any assertion that accepts a PMC type must support the possibility that the PMC type will be null.
I have implemented "null equivalence" -- that is, null==null, for the assertions. I know this can be argued both ways.
Obvious leftovers include the creation of isnt_null and adding null support to the isnt assertions, as well as devising a null policy for the other assertions. The is_deeply seems to do something with null, but that's about it.
(Edited to include my patch number)