code: public String toGroupByString(Criteria criteria, CriteriaQueryBuilder queryBuilder) {
      if(grouped) {
        if(absolute) {
          return path;
        } else {
          return queryBuilder.getAbsolutePath(criteria, path);
        }
      }
      return null;
    }
docs: /*
  @see org.criteria4jpa.projection.Projection#toGroupByString(org.criteria4jpa.Criteria, org.criteria4jpa.impl.CriteriaQueryBuilder)