code: public static <T> T fromJsonString(String json, Class<T> clazz) {
          if (json == null) {
              return null;
          }
          try {
              return JsonUtils.objectMapper.readValue(json, clazz);
          } catch (Exception e) {
              throw new BceClientException("Unable to parse Json String.", e);
          }
      }
docs: Returns the deserialized object from the given json string and target class; or null if the given json string is
  null.