Hi,

I have a working setup with cssnext-loader, but if I require an empty css file, instead of getting an empty string, I am getting a json object.

The problem is at line 30 in index.js:

if (result.css)

should be

if (typeof result.css !== 'undefined')

because result.css is empty, and that's correct, but the check assume there was an error.
If you want, I can make a PR for that.