Error::MissingParameters => write!(f, "Missing parameter"),
            Error::QuestionNotFound => write!(f, "Question not found"),
        }
    }
}

async fn update_question(
    id: String,
    store: Store,
    question: Question,
) -> Result<impl warp::Reply, warp::Rejection> {
    match store.questions.write().await.get_mut(&QuestionId(id)) {
        Some(q) => *q = question,
        None => return Err(warp::reject::custom(Error::QuestionNotFound)),
    }
    Ok(warp::reply::with_status(
        "Question updated",
        StatusCode::OK
    ))
}
...