code: @Override
     public ScatteredConsistentHash union(ScatteredConsistentHash dch1, ScatteredConsistentHash dch2) {
        return dch1.union(dch2);
     }
docs: Merges two consistent hash objects that have the same number of segments, numOwners and hash function.
  For each segment, the primary owner of the first CH has priority, the other primary owners become backups.