docs: @Nullable
      @Size(2)
      static String optCountryCode(
              @NonNull JSONObject jsonObject,
              @NonNull @Size(min = 1) String fieldName) {
          String value = nullIfNullOrEmpty(jsonObject.optString(fieldName));
          if (value != null && value.length() == 2) {
              return value;
          }
          return null;
      }