How to properly check the contents of prefetched data?

export const getStaticProps: GetStaticProps = async (ctx) => {
  const ssg = await createServerSideHelpers({
    router: appRouter,
    ctx: await createContext(),
    transformer: superjson,
  });

  await ssg.public.product.prefetch({
    slug: ctx.params?.slug as string,
  });

  const product = ssg.dehydrate().json.queries[0].state.data;

  if (!product) {
    return {
      notFound: true,
    };
  }

  return {
    props: {
      trpcState: ssg.dehydrate(),
      slug: ctx.params?.slug,
    },
  };
};