Transform java object to JSONObject return null on live server

Question

I have a web application (Maven project, JSP/SERVLET, TomCat 8.5.20). The application run perfectly in localhost (same TomCat version), but when i deploy to a live server, the following code doesn't work, the 'x01Json' (JSONObject) variable value be 'null' after i cal the transfromGameToJson() method.

Game init servlet, where i set JSON in request

        X01Game x01Game = gameController.initX01Game(type, legsNumber, setsNumber, users, doubleIn, doubleOut, x01,
                randomOrder, startingPoint);
        
        JSONObject x01Json = gameController.transfromGameToJson(x01Game);
        
        session.setAttribute("x01Game", x01Game);
        
        request.setAttribute("x01Json", x01Json);
        request.getRequestDispatcher("/darts/x01game.jsp").forward(request, response);

the method

public JSONObject transfromGameToJson(X01Game x01Game) {
    
    ObjectMapper mapper = new ObjectMapper();
    
    try {
        mapper.writeValue(new File("x01Game.json"), x01Game);
        JSONObject object = new JSONObject(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(x01Game));
        return object;
    } catch (JsonGenerationException e) {
        e.printStackTrace();
    } catch (JsonMappingException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    
    return null;
}

Answer 1

If i delete this line from my method, it's working:

      mapper.writeValue(new File("x01Game.json"), x01Game);