docs: private List<Filter> getFilters(final boolean group_by) {
      final int ntags = getNumTags();
      final List<Filter> filters = new ArrayList<Filter>(ntags);
      for (int tag = 0; tag < ntags; tag++) {
        final Filter filter = new Filter();
        filter.tagk = getTagName(tag);
        filter.tagv = getTagValue(tag);
        filter.is_groupby = isTagGroupby(tag);
        if (filter.tagk.isEmpty() || filter.tagv.isEmpty()) {
          continue;
        }
        if (filter.is_groupby == group_by) {
          filters.add(filter);
        }
      }
      // sort on the tagk
      Collections.sort(filters);
      return filters;
    }