code: public Optional<JField> exceptionMessageField() {
          String fieldName = getExceptionMessageFieldName();
          return numericalOrderFields().stream()
                                       .filter(f -> f.name().equals(fieldName) && f.type() == PType.STRING)
                                       .findFirst();
      }
docs: If the message has a 'string' field named 'message', which can be used as the 'message' for exceptions.
  
  @return Optional message field.