SPA mode results in Cannot read properties of null

[jzillmann]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

4.9.2

Plugin version

3.0.0-beta.27

Node.js version

16.18.0

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

12.6

Description

When I enable SPA:

await server.register(FastifyVite, {
  dev: process.argv.includes("--dev"),
  root: import.meta.url,
  spa: true,
});

I'm getting

TypeError: Cannot read properties of null (reading 'routes')
    at Vite.setup (/xxx/node_modules/fastify-vite/mode/development.js:57:35)
    at async Vite.ready (/xxx/node_modules/fastify-vite/index.js:32:55)
    at async file:///xxx/server.js:17:1

Also seems kind of obvious to me that this will always fail looking at development.js:

const loadClient = async () => {
    if (config.spa) {
      return null
    }
...

sync prepareClient (clientModule, scope, config) {
    if (!clientModule) {
      return null
    }
...

return { client, routes: client.routes, handler, errorHandler }

Steps to Reproduce

Enable SPA:

await server.register(FastifyVite, {
  dev: process.argv.includes("--dev"),
  root: import.meta.url,
  spa: true,
});

Expected Behavior

Either enabling SPA should work or there should be a clear instruction on how to set it up.
Would be nice to have a SPA example (preferable in Svelte).