docs: public void aggregateValue(TridentTuple tuple) {
          K key = mapper.getKey(tuple);
          V value = mapper.getValue(tuple);
          V currentValue = aggregateValues.get(key);
          V newValue;
          if (currentValue == null) {
              newValue = aggregator.init(tuple);
          } else {
              newValue = aggregator.combine(currentValue, value);
          }
          LOG.debug("Updating state [{}] ==> [{}]", new Object[]{key, newValue});
          aggregateValues.put(key, newValue);
      }