code: public void accumulate(CollectListData data,
                             Object value) {
          CollectListData.MutableInt counter = data.map.get( value );
          if( counter == null ) {
              counter = new CollectListData.MutableInt();
              data.map.put( value, counter );
          }
          counter.value++;
      }
docs: /* (non-Javadoc)
  @see org.kie.base.accumulators.AccumulateFunction#accumulate(java.lang.Object, java.lang.Object)