Breaks when the source file only contains @at rules.

[flmng0]

Hello!

When processing a source file which only contains at-rules, the plugin breaks.

From my error code and brief skim, it seems to occur from Line 123 of index.js.

The error reported reads as: Cannot read properties of undefined (reading 'source').

The problem file in question is a file from open-props: open-props/media.css.

I will do a workaround and create a pull request once I get home.

Thanks

[argyleink]

this still happening? i'd love a stackblitz or recreatable env for me to test, poke and prod for how to guard or fix the issue 👍🏻