if (!users.containsKey("Admin")) {
            User adminUser = new User("Admin", "123456", 3000, Role.ADMIN);
            users.put(adminUser.getUsername(), adminUser);
        }
        // creating dummy manager
        if (!users.containsKey("Manager")) {
            User manager = new User("Manager", "123456", 3002, Role.MANAGER);
            users.put(manager.getUsername(), manager);
        }