docs: public static SumChartCost create(ChartCost ... filters) {
      List<ChartCost> nonNullFilters = Lists.newArrayList();
      for (ChartCost filter : filters) {
        if (filter != null) {
          nonNullFilters.add(filter);
        }
      }
      
      if (nonNullFilters.size() > 0) {
        return new SumChartCost(nonNullFilters);
      } else {
        return null;
      }
    }