Empty @layer declaration leads to Cannot read properties of undefined (reading 'length)')

[GreenTea124]

Bug report

You should be able to define CSS layers like this:

@layer ui-components;

And like this:

@layer ui-components {
}

Actual Behavior

2nd syntax works fine, 1st syntax leads to this error:

ERROR in _webpack/css/867a6d3b57e2ee85e279.css
_webpack/css/867a6d3b57e2ee85e279.css from Css Minimizer plugin
TypeError: Cannot read properties of undefined (reading 'length')
    at equals (C:\Users\xyz\node_modules\postcss-discard-duplicates\src\index.js:72:36)
    at dedupe (C:\Users\xyz\node_modules\postcss-discard-duplicates\src\index.js:148:7)
    at OnceExit (C:\Users\xyz\node_modules\postcss-discard-duplicates\src\index.js:161:7)
    at LazyResult.runAsync (C:\Users\xyz\node_modules\postcss\lib\lazy-result.js:326:21)
    at async cssnanoMinify (eval at transform (C:\Users\xyz\node_modules\css-minimizer-webpack-plugin\dist\minify.js:67:28), <anonymous>:78:18)
    at async minify (C:\Users\xyz\node_modules\css-minimizer-webpack-plugin\dist\minify.js:33:26)
webpack-web 

Expected Behavior

Both syntaxes should work.

Please paste the results of npx webpack-cli info here, and mention other relevant information

  System:
    OS: Windows 10
  Binaries:
    Node: 18.16.0 - C:\Program Files\nodejs\node.EXE
    npm: 9.7.2 - C:\Program Files\nodejs\npm.CMD

[ludofischer]

This might be fixed by updating cssnano to 6.0.4. Unfortunately, I would need the exact code sample triggering the error to verify it is really fixed.