code: public Double getGroupingDouble(String label) {
          PrimitiveObject o = getPrimitiveObject(KEY, label, ObjectUtil.DOUBLE, "Double");
          if (o == null) {
              return null;
          }
          return (Double) o.getObject();
      }
docs: Get grouping {@link Double} value
  @param label target label
  @return {@link Double} value of the label. If it is not null.