docs: public Object getAggregatedValue(Session session, Object currValue) {
  
          if (currValue == null) {
              // A VoltDB extension APPROX_COUNT_DISTINCT
              return opType == OpTypes.COUNT || opType == OpTypes.APPROX_COUNT_DISTINCT ?
                      ValuePool.INTEGER_0: null;
              /* disable 2 lines...
              return opType == OpTypes.COUNT ? ValuePool.INTEGER_0
                                             : null;
              ...disabled 2 lines */
              // End of VoltDB extension
          }
  
          return ((SetFunction) currValue).getValue();
      }