Adding CSS to the vendor bundle via bundleCSS is broken

[Miercko]

Using this

"vendor": {
      "bundleCSS": [
        "@fortawesome/fontawesome-free/css/all.css"
      ],
      "includeStaticFiles": []
    }

will break the build with the following error:

ERROR in chunk vendor [initial]
assets/css/vendor.bundle.css
Cannot read property 'pop' of undefined
ℹ ｢wdm｣: Failed to compile.

This seams to be related to:

• "Cannot read property 'pop' of undefined" with a common cache group webpack-contrib/mini-css-extract-plugin#257
• Cannot read property 'pop' of undefined webpack-contrib/mini-css-extract-plugin#341