code: public static <T> Map<String, T> toLowerCaseKeys(Map<String, T> map) {
          Map<String, T> res = new HashMap<>();
          for (Map.Entry<String, T> entry : map.entrySet()) {
              res.put(entry.getKey().toLowerCase(), entry.getValue());
          }
          return res;
      }
docs: Returns a copy of the given map with lowercase keys
  @param map the map to convert
  @return copy of map with lowercase keys