After upgrading to Next.js 13, we started seeing the following HMR
errors:
```sh
$ next dev
# ...
warn - Fast Refresh had to perform a full reload. Read more: https://nextjs.org/docs/basic-features/fast-refresh#how-it-works
TypeError: Cannot read properties of null (reading 'length')
at eval (webpack-internal:///./node_modules/next/dist/client/dev/error-overlay/hot-dev-client.js:262:55)
```
This error appears related to the changes made in
https://github.com/vercel/next.js/pull/42350 (cc @alexkirsz). It appears
that `module.hot.check` will pass `null` when there are no updates:
```ts
/**
* Throws an exceptions if status() is not idle.
* Check all currently loaded modules for updates and apply updates if found.
* If no update was found, the callback is called with null.
* If autoApply is truthy the callback will be called with all modules that were disposed.
* apply() is automatically called with autoApply as options parameter.
* If autoApply is not set the callback will be called with all modules that will be disposed on apply().
* @param autoApply
*/
check(autoApply?: boolean): Promise<null|ModuleId[]>;
```
When `updatedModules` is `null`, we skip the `apply()` call as this was
producing `apply() is only allowed in ready status (state: idle)`
errors. This matches [the prior behavior when `autoApply` was
enabled](8241da7f1e/lib/hmr/HotModuleReplacement.runtime.js (L266-L272)).
Fixes#43143. Also reported on Stack Overflow:
-
https://stackoverflow.com/questions/74415937/nextjs-typeerror-cannot-read-properties-of-null-reading-length
-
https://stackoverflow.com/questions/74504229/nextjs-v-13-typeerror-cannot-read-properties-of-null-reading-length
I tested this change locally and no longer see these HMR errors.
## Bug
- [X] Related issues linked using `fixes #number` - no related issues
- [X] Integration tests added - there aren't any existing tests, afaict
- [X] Errors have a helpful link attached, see `contributing.md` - N/A
Co-authored-by: JJ Kasper <jj@jjsweb.site>
ed2aa9fd75