Describe the bug
When a CSS entry point is added to package.json, webpack generates an empty .js file. For example, adding the entry "style": "./assets/css/style.css" outputs css/style.css 20 bytes js/style.js 0 bytes.

More info about this can be read in the issues webpack-contrib/mini-css-extract-plugin#151 and webpack-contrib/extract-text-webpack-plugin#518.

Steps to Reproduce

1. Create a new npm project running npm init
2. Install 10up-toolkit running npm install --save-dev 10up-toolkit
3. Create a CSS file and add an entry point in package.json

...
"10up-toolkit": {
  "entry": {
   "style": "./assets/css/style.css"
  },
...

4. Run 10up-toolkit build
5. Check at the dist folder the files style.css and style.js

Expected behavior
Empty scripts removed from output.

Screenshots

Environment information

• Device:
• OS:
• Browser and version:
• WordPress version:

• Plugins and version:
• Theme and version:

• Site Health Info:

Additional context
A possible workaround is importing CSS file into a JS file. However, there are cases when CSS doesn't have a correspondent JS file.