Plan difference between cbas and *DB

While working on MB-55865, I noticed that the bug only happened while running the cbas code and did not happen while running in *DB.

The following query (with CBO turned off) produced an "inapplicable hash join hint" warning on cbas, but not on *DB.

SELECT COUNT(DISTINCT n.n_name) FROM customer c JOIN nation n

ON c.c_nationkey /*+ hashjoin build (n) */ = n.n_nationkey;

On debugging further, I saw that on the cbas side (running from the cbas gui), the join has projects on both sides, so varsRight in JoinUtils::setJoinAlgorithmAndExchangeAlgo() does not have $n and we generate the warning saying cannot build with n.
On the asterix side, (running from *DB gui and our test framework), there are no projects, so we see $n in the varsRight, so no warning is generated as we can build with n.