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