Registering an auxiliary equivalence predicate with NULL on one side would
be incorrect, because <expr> = NULL is false (even NULL = NULL).
Change-Id: Ie10d0e2fa61e5c2c7d4040c8b78d5bfb1a1e2761
Reviewed-on: http://gerrit.cloudera.org:8080/777
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: Internal Jenkins