Подтягивайтесь разрабы к вам претензия. Думаю многие меня подержат.

public static void main(String[] args) {
        //you can find your_file_name.tmp in your TMP directory or fix outputStream/inputStream according to your real file location
        //вы можете найти your_file_name.tmp в папке TMP или исправьте outputStream/inputStream в соответствии с путем к вашему реальному файлу
        try {
            File your_file_name = File.createTempFile("your_file_name", null, new File("C:\\Program Files\\Java\\JavaRushTasks\\2.JavaCore\\src\\com\\javarush\\task\\task20\\task2002"));
            OutputStream outputStream = new FileOutputStream(your_file_name);
            InputStream inputStream = new FileInputStream(your_file_name);

            JavaRush javaRush = new JavaRush();
            //initialize users field for the javaRush object here - инициализируйте поле users для объекта javaRush тут
            User user = new User();
            user.setBirthDate(null);
            user.setCountry(User.Country.OTHER);
            user.setFirstName("Vasy");
            user.setLastName("");
            user.setMale(true);

            /*User user = new User();
            user.setBirthDate(new Date());
            user.setCountry(User.Country.OTHER);
            user.setFirstName("Vasy");
            user.setLastName("Petrov");
            user.setMale(true);*/

            javaRush.users.add(user);

            javaRush.save(outputStream);
            outputStream.flush();

            JavaRush loadedObject = new JavaRush();
            loadedObject.load(inputStream);
            //check here that javaRush object equals to loadedObject object - проверьте тут, что javaRush и loadedObject равны
            System.out.println(javaRush.equals(loadedObject));

            outputStream.close();
            inputStream.close();

        } catch (IOException e) {
            //e.printStackTrace();
            System.out.println("Oops, something wrong with my file");
        } catch (Exception e) {
            //e.printStackTrace();
            System.out.println("Oops, something wrong with save/load method");
        }
    }

    public static class JavaRush {
        public List<User> users = new ArrayList<>();

        public void save(OutputStream outputStream) throws Exception {
            //implement this method - реализуйте этот метод
            PrintWriter pw = new PrintWriter(outputStream);
            String isListPresent = !(users.isEmpty()) ? "yes" : "no";
            pw.println(isListPresent);
            if (!(users.isEmpty())) {
                for (User a : users) {
                    String firstName = a.getFirstName() == null ? "null" : a.getFirstName();
                    pw.println(firstName);
                    String lastName = a.getLastName() == null ? "null" : a.getLastName();
                    pw.println(lastName);
                    String date = a.getBirthDate() == null ? "null" : String.valueOf(a.getBirthDate().getTime());
                    pw.println(date);
                    pw.println(a.isMale());
                    String country = a.getCountry() == null ? "null" : a.getCountry().getDisplayedName();
                    pw.println(country);
                }
            }
            pw.flush();
        }

        public void load(InputStream inputStream) throws Exception {
            //implement this method - реализуйте этот метод
            BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
            String isListPresent = br.readLine();
            if (isListPresent.equals("yes")) {
                User user = new User();
                while (br.ready()) {


                    String firstName;
                    if ((firstName = br.readLine()).equals("null"))
                        user.setFirstName(null);
                    else
                        user.setFirstName(firstName);

                    String lastName;
                    if ((lastName = br.readLine()).equals("null"))
                        user.setLastName(null);
                    else
                        user.setLastName(lastName);


                    /*String date = br.readLine();
                    SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd HH:mm:ss zzz yyyy", Locale.ENGLISH);
                    user.setBirthDate(sdf.parse(date));*/
                    String date;
                    if ((date = br.readLine()).equals("null"))
                        user.setBirthDate(null);
                    else
                        user.setBirthDate(new Date(Long.parseLong(date)));

                    String isMail = br.readLine();
                    user.setMale(Boolean.valueOf(isMail));
                    /*if (isMail.equals("true")) {
                        user.setMale(true);
                    }
                    else if (isMail.equals("false")) {
                        user.setMale(false);
                    }*/

                    String country;
                    if ((country = br.readLine()).equals("null"))
                        user.setCountry(null);
                    //System.out.println(country);
                    /*if (country != null)
                        user.setCountry(User.Country.valueOf(country));
                    else
                        user.setCountry(null);*/
                    else {
                        switch (country) {
                            case "Ukraine":
                                user.setCountry(User.Country.UKRAINE);
                                break;
                            case "Russia":
                                user.setCountry(User.Country.RUSSIA);
                                break;
                            case "Other":
                                user.setCountry(User.Country.OTHER);
                                break;
                        }
                    }
                users.add(user);
                }

            }
            br.close();
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            JavaRush javaRush = (JavaRush) o;

            return users != null ? users.equals(javaRush.users) : javaRush.users == null;

        }

        @Override
        public int hashCode() {
            return users != null ? users.hashCode() : 0;
        }
    }
}