fix: applying plugin on an empty css file

[AloisSeckar]

Yesterday, I am trying to add @nuxt/fonts module into my project where I already integrated Open Props using postcss-jit-props plugin. It turned out the plugin cannot handle empty css file (.nuxt/nuxt-fonts-global.css) that is auto-generated by @nuxt/fonts module and is empty when you don't specify any global font-family (which is common use case - fonts can be injected into CSS locally only where you need them).

The error was:

ERROR  Internal server error: [postcss] Cannot read properties of undefined (reading 'source')                                                   22:25:52  
  Plugin: vite:css
  File: C:/Programming/Git/nuxt-ignis/.nuxt/nuxt-fonts-global.css:undefined:NaN
      at Object.Once (C:\Programming\Git\nuxt-ignis\node_modules\.pnpm\postcss-jit-props@1.0.15_postcss@8.4.49\node_modules\postcss-jit-props\index.js:130:88)
      at LazyResult.runOnRoot (C:\Programming\Git\nuxt-ignis\node_modules\.pnpm\postcss@8.5.1\node_modules\postcss\lib\lazy-result.js:327:23)
      at LazyResult.runAsync (C:\Programming\Git\nuxt-ignis\node_modules\.pnpm\postcss@8.5.1\node_modules\postcss\lib\lazy-result.js:258:26)
      at LazyResult.async (C:\Programming\Git\nuxt-ignis\node_modules\.pnpm\postcss@8.5.1\node_modules\postcss\lib\lazy-result.js:160:30)
      at LazyResult.then (C:\Programming\Git\nuxt-ignis\node_modules\.pnpm\postcss@8.5.1\node_modules\postcss\lib\lazy-result.js:404:17)

This lead me to this repo and to index.js file implementation.

When I added null checks for node.first my error disappeared (while Open Props are still being injected as expected).

To have a quick fix working for me, I made a fork and created custom NPM package elrh-postcss-jit-props, but I believe it would be better to have it here in the official repo.

I also added test as a POC (if you remove the null checks, it starts failing).

If I did something wrong, I am happy to hear a feedback.

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[argyleink]

looks good, thanks for the added test!