如何处理 nullPointerException

问：

public List<PostResponse> getAllPosts(Optional<Long> userId) {
    List<Post> list;
    if (userId.isPresent())
        list = postRepository.findByUserId(userId.get());

    list = postRepository.findAll();
    return list.stream().map(p -> {
        List<LikeResponse> likes = likeService.getAllLikesWithParam(Optional.ofNullable(null), Optional.of(p.getId()));
        return new PostResponse(p, likes);}).collect(Collectors.toList());
}



public List<LikeResponse> getAllLikesWithParam(Optional<Long> userId, Optional<Long> postId) {
    List<Like> list;
    if(userId.isPresent() && postId.isPresent()) {
        list = likeRepository.findByUserIdAndPostId(userId.get(), postId.get());
    }else if(userId.isPresent()) {
        list = likeRepository.findByUserId(userId.get());
    }else if(postId.isPresent()) {
        list = likeRepository.findByPostId(postId.get());
    }else
        list = likeRepository.findAll();
    return list.stream().map(like -> new LikeResponse(like)).collect(Collectors.toList());
}

我在这一行的 getAllPosts 中出错 Optional.ofNullable（null） 错误是：java.lang.NullPointerException：null