Single Fetch: returning null from resource route loader leads to error

[chrisvariety]

Reproduction

https://stackblitz.com/edit/remix-run-remix-xsdwha?file=app%2Froutes%2F_index.tsx

Just this triggers it when you don't have a default export (making it a resource route)

export const loader = async () => {
  return null;
};

System Info

System:
    OS: macOS 14.0
    CPU: (10) arm64 Apple M1 Pro
    Memory: 62.27 MB / 32.00 GB
    Shell: 3.6.1 - /usr/local/bin/fish
  Binaries:
    Node: 20.11.0 - ~/.volta/tools/image/node/20.11.0/bin/node
    npm: 10.2.4 - ~/.volta/tools/image/node/20.11.0/bin/npm
  Browsers:
    Chrome: 120.0.6099.109
    Safari: 17.0
  npmPackages:
    @remix-run/dev: ^2.9.2 => 2.9.2
    @remix-run/eslint-config: ^2.9.2 => 2.9.2
    @remix-run/node: ^2.9.2 => 2.9.2
    @remix-run/react: ^2.9.2 => 2.9.2
    @remix-run/serve: ^2.9.2 => 2.9.2
    vite: ^5.2.11 => 5.2.11

Used Package Manager

npm

Expected Behavior

It does not error.

Actual Behavior

Seeing this in Stackblitz:

Unexpected Server Error

TypeError: response is not an Object. (evaluating 'router.UNSAFE_DEFERRED_SYMBOL in response')

Seeing this locally (node v20)

[remix] TypeError: Cannot use 'in' operator to search for 'Symbol(deferred)' in null
[remix]     at handleResourceRequest (/Users/chrismcc/workspace/atlas/node_modules/@remix-run/server-runtime/dist/server.js:371:60)
[remix]     at async requestHandler (/Users/chrismcc/workspace/atlas/node_modules/@remix-run/server-runtime/dist/server.js:138:18)
[remix]     at async nodeHandler (/Users/chrismcc/workspace/atlas/node_modules/@remix-run/dev/dist/vite/plugin.js:841:27)
[remix]     at async /Users/chrismcc/workspace/atlas/node_modules/@remix-run/dev/dist/vite/plugin.js:844:15

Looks like this stems from this because typeof null === 'object:

remix/packages/remix-server-runtime/server.ts

Lines 594 to 600 in 2e65318

	if (typeof response === "object") {
	invariant(
	!(DEFERRED_SYMBOL in response),
	`You cannot return a \`defer()\` response from a Resource Route. Did you ` +
	`forget to export a default UI component from the "${routeId}" route?`
	);
	}

[dmarkow]

Hitting this as well when trying to use unstable_singleFetch. Using the json wrapper doesn't work either, as return json(null) gives a typescript error:

Argument of type '({ request }: LoaderArgs) => Promise<TypedResponse<null>>' is not assignable to parameter of type 'Loader'.
  Type 'Promise<TypedResponse<null>>' is not assignable to type 'MaybePromise<DataFunctionReturnValue>'.
    Type 'Promise<TypedResponse<null>>' is not assignable to type '{ [key: string]: Serializable; [key: number]: Serializable; [key: symbol]: Serializable; } | Map<Serializable, Serializable> | Set<...> | Promise<...> | Promise<...>'.
      Type 'Promise<TypedResponse<null>>' is not assignable to type 'Promise<Serializable>'.
        Type 'TypedResponse<null>' is not assignable to type 'Serializable'.
          Type 'TypedResponse<null>' is not assignable to type '{ [key: string]: Serializable; [key: number]: Serializable; [key: symbol]: Serializable; }'.
            Property 'headers' is incompatible with index signature.
              Type 'Headers' is not assignable to type 'Serializable'.
                Type 'Headers' is not assignable to type '{ [key: string]: Serializable; [key: number]: Serializable; [key: symbol]: Serializable; }'.
                  Index signature for type 'string' is missing in type 'Headers'.```

[brophdawg11]

This should be resolved in the next release via #9488

[github-actions]

🤖 Hello there,

We just published version 2.10.0-pre.0 which involves this issue. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[github-actions]

🤖 Hello there,

We just published version 2.10.0 which involves this issue. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!