java.lang.NullPointerException

Boa noite.

Será que alguém pode me ajudar?

Estou tentando rodar o teste abaixo ele sempre retorna '"main" java.lang.NullPointerException: ' para o meu objeto no for mesmo tendo dados no banco e objeto estando setado.

TestaUserType.java

public class TestaUserType
{
    public static void main(String[] args) throws SQLException
    {
        Database database = new Database();

        try(Connection connection = database.getConnection()) {
            List<UserTypes> userTypes = new UserTypesDAO(connection).list();

            for (UserTypes userType : userTypes) {
                System.out.println("Tipos cadastrados: " + userType.getTitle());
                UsersDAO usersDAO = new UsersDAO(connection);

                for(User user : usersDAO.search(userType)) {
                    System.out.println(user);
                }
            }
        }
    }
}

UsersDAO.java

public class UsersDAO
{
    private Connection con;

    public UsersDAO(Connection con)
    {
        this.con = con;
    }

    public void save(User user) throws SQLException
    {
        String SQL = "INSERT INTO `users`(`name`, `email`, `password`, `created_at`)";
                SQL += " VALUES(?, ?, ?, ?)";

        try ( PreparedStatement stmt = con.prepareStatement(SQL, Statement.RETURN_GENERATED_KEYS) ) {

            Timestamp date = new Timestamp(new Date().getTime());

            stmt.setString(1, user.getName());
            stmt.setString(2, user.getEmail());
            stmt.setString(3, user.getPassword());
            stmt.setTimestamp(4, date);
            stmt.execute();

        }
    }

    public List<User> list() throws SQLException
    {
        List<User> users = new ArrayList<>();
        String SQL = "SELECT * FROM users";

        try(PreparedStatement stmt = con.prepareStatement(SQL)) {
            stmt.execute();
            getResult(users, stmt);
        }

       return users;
    }

    public List<User> search(UserTypes userType) throws SQLException
    {
        List<User> users = new ArrayList<>();
        String SQL = "SELECT * FROM users WHERE type_id = ?";

        try(PreparedStatement stmt = con.prepareStatement(SQL)) {
            stmt.setInt(1, userType.getId());
            stmt.execute();

            getResult(users, stmt);
        }

        return null;
    }

    private void  getResult(List<User> users, PreparedStatement stmt) throws SQLException
    {
        try(ResultSet resultSet = stmt.getResultSet()) {
            while( resultSet.next() ) {
                String name = resultSet.getString("name");
                String email = resultSet.getString("email");
                String password = resultSet.getString("password");
                User user = new User(name, email, password);

                users.add(user);
            }
        }
    }
}

UserTypes.java

public class UserTypes
{
    private final Integer id;
    private final String title;

    public UserTypes(Integer id, String title)
    {
        this.id = id;
        this.title = title;
    }

    public Integer getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

}

Desde já, obrigado :)