From: Darren King <darrenk@insightdist.com>

From: Darren King <darrenk@insightdist.com>

I have always been under the impression that NULL is not equal to
NULL and that NULL is not equal to anything else either.  If this
is the case, then this patch is correct.

If NULL _is_ equal to NULL, then I think there are other problems
in the Group By logic.