code: public static Set<String> mergeMVFieldValues(Collection<String>  currValueSet,
                                                   Collection<String>  removeValueSet,
                                                   Collection<String>  newValueSet) {
          Set<String> resultSet = new HashSet<>();
          if (currValueSet != null) {
              resultSet.addAll(currValueSet);
          }
          if (removeValueSet != null) {
              resultSet.removeAll(removeValueSet);
          }
          if (newValueSet != null) {
              resultSet.addAll(newValueSet);
          }
          return resultSet;
      }
docs: Merge the given current, remove, and new MV field values into a new set.