fix(builder): returns empty object instead undefined

[qramilq]

The result of function applyReactShims is passing to rsbuildReal.mergeRsbuildConfig which then make destruction when trying normalize config structure. So undefined can't be destructed.

Maybe we should add condition and not pass result of applyReactShims to rsbuildReal.mergeRsbuildConfig if it returns undefined or we need to add conditions in normalizeConfigStructure?

[netlify]

✅ Deploy Preview for storybook-rsbuild ready!

Name	Link
🔨 Latest commit	5faa594
🔍 Latest deploy log	https://app.netlify.com/projects/storybook-rsbuild/deploys/690219057faa310008f4af3f
😎 Deploy Preview	https://deploy-preview-370--storybook-rsbuild.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[fi3ework]

thank you for your contributing, i'm not sure whether undefined equals to {} when merging config (i think so, so it's writen like this now). have you ever encounter specific issue with the code changed in this PR? generally, LGTM.

[qramilq]

@fi3ework thank's for reviewing. I passed {}, because it can be destructing without errors:

const configObject = {}
const configUndefined = undefined

const {dev, output} = configObject //  <- Ok
const {dev, output} = configUndefined //  <- Error

How I find this: I installed the rslib and chose to also install the storybook during installation. I didn't change code which was generated by installer. When I try to launch the storybook (using npm run storybook), I get an error:

You can try it yourself, just make steps from rslib's guide, just choose react+typescript+storybook

[fi3ework]

oh. i think it's introduced in web-infra-dev/rsbuild#6369. returning undefined appears to be exploiting a bug to run in the past. an empty object is the correct way. thank you for your contribution.