impl Question {
    fn new(
        id: QuestionId,
        title: String,
        content: String,
        tags: Option<Vec<String>>
    ) -> Self {
        Question {
            id,
            title,
            content,
            tags,
        }
    }
}
...
#[derive(Debug)]
struct InvalidId;
impl Reject for InvalidId {}

impl FromStr for QuestionId {
    type Err = std::io::Error;

    fn from_str(id: &str) -> Result<Self, Self::Err> {
        match id.is_empty() {