code: private Map<String, Integer> parseMinDays(JsonObject root) {
      JsonObject node = resolve(root, "supplemental", "weekData", "minDays");
      Map<String, Integer> m = new HashMap<>();
      for (String key : objectKeys(node)) {
        m.put(key, Integer.valueOf(string(node, key)));
      }
      return m;
    }
docs: Parse the "min days" values. This indicates the minimum number of days
  a week must include for it to be counted as the first week of the year;
  otherwise it's the last week of the previous year.