Все работает корректно, но валидация не проходит для второго пункта

public void save(OutputStream outputStream) throws Exception {
            PrintWriter writer = new PrintWriter(outputStream);
            //users.forEach(u -> System.out.println(u.getFirstName() + " " + u.getLastName() + " " + u.getBirthDate() + " " + u.getCountry().getDisplayedName() + " " + u.isMale()));
            String isAssetsEmpty = this.users.isEmpty() ? "yes" : "no";
            writer.println(isAssetsEmpty);

            if (!this.users.isEmpty()) {
                writer.println(this.users.size());
                for (User user : this.users) {
                    writer.println(user.getFirstName() == null ? "null" : user.getFirstName());
                    writer.println(user.getLastName() == null ? "null" : user.getLastName());
                    writer.println(user.getBirthDate() == null ? 0 : user.getBirthDate().getTime());
                    writer.println(user.getCountry() == null ? "null" : user.getCountry().getDisplayedName());
                    writer.println(user.isMale());

                }
            }

            writer.flush();
        }

        public void load(InputStream inputStream) throws Exception {
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

            String isAssetsEmpty = reader.readLine();
            if (isAssetsEmpty.equals("no")) {
                int usersCount = Integer.parseInt(reader.readLine());
                List<User> assets = new ArrayList<>();
                for (int i = 0; i < usersCount; i++) {
                    User asset = new User();
                    String firstName = reader.readLine();
                    if (!(firstName.equals("null"))) asset.setFirstName(firstName);
                    String lastName = reader.readLine();
                    if (!(lastName.equals("null"))) asset.setLastName(lastName);
                    Long date = Long.parseLong(reader.readLine());
                    if (!(date == 0)) {
                        Date birthDay = new Date();
                        birthDay.setTime(date);
                        asset.setBirthDate(birthDay);
                    }
                    String country = reader.readLine();
                    if (!(country.equals("null"))) switch (country) {
                        case "Russia": asset.setCountry(User.Country.RUSSIA);
                        break;
                        case "Ukraine": asset.setCountry(User.Country.UKRAINE);
                        break;
                        case "Other": asset.setCountry(User.Country.OTHER);
                        break;
                    }
                    boolean male = Boolean.parseBoolean(reader.readLine());
                    asset.setMale(male);
                    assets.add(asset);
                }
                //assets.forEach(u -> System.out.println(u.getFirstName() + " " + u.getLastName() + " " + u.getBirthDate() + " " + u.getCountry().getDisplayedName() + " " + u.isMale()));
                this.users = assets;
            }
        }