When `getStaticProps` or `getServerSideProps` returned props containing
non-JSON-serializable values (e.g. `Date`, `Map`, class instances), vinext
silently rendered an empty page instead of surfacing an error. This ports
Next.js's `isSerializableProps` check from `packages/next/src/lib/is-serializable-props.ts`
and invokes it from `pages-page-data.ts` and `dev-server.ts` after the
redirect/notFound short-circuits, mirroring `render.tsx` (~lines 982 and
1200). The thrown `SerializableError` is caught by the existing per-request
error boundary, which returns a 500 with a Next.js-style message naming the
offending key.
James Anderson