BeanToCsv not writing to csv file

Question

I'm working on writing a method for my discord bot that writes all the member data to a csv` file.

However, I'm struggling to do so using BeanToCsv. The only output to the file is the headers and nothing else. I am able to get each field from each object as seen with the prints, each field is a String.

I previously used a CSVWriter which worked, but opted for the ability to write object data instead.

public static void generateNewCSV(GuildMessageReceivedEvent event) throws IOException, CsvDataTypeMismatchException, CsvRequiredFieldEmptyException
    {
        Writer writer = new FileWriter(MEMBER_DATA_FILE_PATH);

        List<User> users = new ArrayList<User>();

        for(Member mem : event.getGuild().getMembers()) {
            users.add(new User("\"" + mem.getUser().getId() + "\"", mem.getUser().getName(), mem.getEffectiveName(), mem.getRoles().toString()));
            //          System.out.println("id : " + users.get(users.size()-1).getUserId());
//          System.out.println("name : " + users.get(users.size()-1).getUserName());
//          System.out.println("nickname : " + users.get(users.size()-1).getUserNickname());
//          System.out.println("roles : " + users.get(users.size()-1).GetUserRoles());
//          System.out.println( "=============================");
        }

        ColumnPositionMappingStrategy<User> strategy = new ColumnPositionMappingStrategy<User>();
        strategy.setType(User.class);
        String[] columns = {"id", "name", "nickname", "roles"};
        strategy.setColumnMapping(columns);

        StatefulBeanToCsv<User> beanToCsv = new StatefulBeanToCsvBuilder<User>(writer)
                .build(); 


        beanToCsv.write(users);
        writer.close();
        users.clear();
        System.out.println("save complete");
    }

The only output to the csv file is the given headers, but nothing else. It is supposed to write all the information obtained from the created user object.