code: public Map<String, Object> fromJson(String json) throws IOException {
      if (json == null) {
        throw new IllegalArgumentException("json == null");
      }
      if (json.length() == 0) {
        throw new IllegalArgumentException("json empty");
      }
      return fromJson(new StringReader(json));
    }
docs: Deserializes the specified json into a {@link Map}. If you have the Json in a {@link Reader}
  form instead of a {@link String}, use {@link #fromJson(Reader)} instead.