Not returning from loader results in unexpected error

[heivo]

I'm using React Router as a...

framework

Reproduction

I have a route where I forgot to return in a loader function. This wasn't a problem unless I upgraded from 7.4.1 to 7.5.3

After the upgrade there is an error in the browser:

TypeError: Cannot use 'in' operator to search for 'error' in undefined
    at unwrapSingleFetchResult (http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:7742:15)
    at http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:7559:20
    at async dataRoute.loader (http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:8059:24)
    at async http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:7557:24
    at async http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:5135:19
    at async callLoaderOrAction (http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:5187:16)
    at async Promise.all (index 1)
    at async singleFetchLoaderNavigationStrategy (http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:7581:3)
    at async callRouteMiddleware (http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:4901:37)
    at async runMiddlewarePipeline (http://localhost:3000/node_modules/.vite/deps/chunk-X5OJKGOA.js?v=706cb39c:4867:18)

When I add a return null in the loader the error is gone. The loader is only used for authentication, that's why I don't return data.

System Info

System:
    OS: Linux 6.11 Ubuntu 24.04.2 LTS 24.04.2 LTS (Noble Numbat)
    CPU: (16) x64 AMD Ryzen 9 PRO 7940HS w/ Radeon 780M Graphics
    Memory: 12.41 GB / 29.99 GB
    Container: Yes
    Shell: 5.9 - /usr/bin/zsh
  Binaries:
    Node: 22.13.0 - /run/user/1000/fnm_multishells/6679_1745822615001/bin/node
    npm: 10.9.2 - /run/user/1000/fnm_multishells/6679_1745822615001/bin/npm
    pnpm: 9.11.0 - ~/.local/share/pnpm/pnpm
  Browsers:
    Chrome: 134.0.6998.165
  npmPackages:
    @react-router/dev: ^7.5.3 => 7.5.3 
    @react-router/express: ^7.5.3 => 7.5.3 
    @react-router/node: ^7.5.3 => 7.5.3 
    react-router: ^7.5.3 => 7.5.3 
    vite: ^6.2.2 => 6.3.1

Used Package Manager

npm

Expected Behavior

Either not returning is allowed or error with a meaningful message is thrown.

Actual Behavior

An error occurs in the browser when trying to unwrap the loader data: TypeError: Cannot use 'in' operator to search for 'error' in undefined

[brophdawg11]

I am pretty sure this is the same issue that was fixed by #13496 and will be available in the next release. If you want to confirm, it should be in the nightly release tag (npx upgrade-remix nightly -f)

[heivo]

I can confirm it's fixed in the nightly build, thanks alot!

[iyhub]

seems loader function must have a return an object {}