code: public static Map<String, Object> camelToUnderline(Map<String, Object> map) {
          Map<String, Object> newMap = new HashMap<>();
          for (String key : map.keySet()) {
              newMap.put(camelToUnderline(key), map.get(key));
          }
          return newMap;
      }
docs: string keys are converted from camel style to underline style. a new map is returned, the original map is not changed.