Hello, I've been trying to migrate to using the app router, but one hurdle I've ran into is how to replicate getServerSideProps' notFound response. Basically, if I have a route such as /[id]/page.tsx, not every ID is going to actually exist, so I'd like to send a 404 response in that case.

Before, I would do something like:

export const getServerSideProps = (context) => {
    if(/* check if context.params.id doesn't exist */) {
        return { notFound: true };
    }

    // Handle everything else...
};

How do I do this with app router?