Currently, ConsistentHash.getPrimarySegmentsForOwner(Address) throws an IllegalArgumentException if the address is not a member of the consistent hash.

Following a partition -> merge, a member can receive a topology change event that includes an old consistent hash for which the local address is not a member.  When querying the consistent hash, I would expect the local member should not own any segments in the old hash, and thus getPrimarySegmentsForOwner(...) should return an empty set.  There's nothing "illegal" about the address, thus throwing an IAE is not really appropriate, IMO.