Prerendering causing build error in SvelteKit

Environment

  System:
    OS: Windows 11 10.0.22621
    CPU: (12) x64 AMD Ryzen 5 3600 6-Core Processor
    Memory: 6.26 GB / 15.91 GB
  Binaries:
    Node: 18.18.2 - C:\Program Files\nodejs\node.EXE
    npm: 10.2.3 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Chromium (120.0.2210.144)
    Internet Explorer: 11.0.22621.1
  npmPackages:
    @auth/core: ^0.23.0 => 0.23.0
    @auth/sveltekit: ^0.9.0 => 0.9.0

Reproduction URL

https://github.com/WhyAsh5114/authjs-sveltekit-prerender

Describe the issue

Marking a route as prenderable with export const prerender = true creates a build error, usable in dev though. Removing the prerender line fixes it.

TypeError: Cannot read properties of undefined (reading 'length')
    at Object.handle (file:///D:/Programming/Web/authjs-sveltekit-prerender/.svelte-kit/output/server/chunks/hooks.server.js:49:24)
    at respond (file:///D:/Programming/Web/authjs-sveltekit-prerender/.svelte-kit/output/server/index.js:2650:43)
    at async visit (file:///D:/Programming/Web/authjs-sveltekit-prerender/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:202:20)

node:internal/event_target:1033
  process.nextTick(() => { throw err; });
                           ^
Error: 500 /prerender
To suppress or handle this error, implement `handleHttpError` in https://kit.svelte.dev/docs/configuration#prerender
    at file:///D:/Programming/Web/authjs-sveltekit-prerender/node_modules/@sveltejs/kit/src/core/config/options.js:202:13
    at file:///D:/Programming/Web/authjs-sveltekit-prerender/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:65:25
    at save (file:///D:/Programming/Web/authjs-sveltekit-prerender/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:403:4)
    at visit (file:///D:/Programming/Web/authjs-sveltekit-prerender/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:236:3)
Emitted 'error' event on Worker instance at:
    at [kOnErrorMessage] (node:internal/worker:300:10)
    at [kOnMessage] (node:internal/worker:311:37)
    at MessagePort.<anonymous> (node:internal/worker:212:57)
    at [nodejs.internal.kHybridDispatch] (node:internal/event_target:757:20)
    at exports.emitMessage (node:internal/per_context/messageport:23:28)

Node.js v18.18.2

How to reproduce

1. Initialize new SvelteKit project, install @auth/sveltekit and @auth/core.
2. Setup the handle hook with SvelteKitAuth()
3. Create a prerenderable route, exclude it from validation in the root layout so it's accessible even if not logged in.
4. Try building with npm run build.

Expected behavior

Build should succeed.

Start with the linked reproduction repository and follow the listed setup steps, then run npm run build with the prerenderable route enabled. Use the reported failure in .svelte-kit/output/server/chunks/hooks.server.js and the prerender stack trace to trace the build path; done means the build succeeds with export const prerender = true.