return empty array when no match

Author: forsartis

purgecss/index.js

@@ -2,7 +2,7 @@ const postcss = require('postcss');
 
 let config = {
   content: ['./public/**/*.html', './src/**/*.vue'],
-  defaultExtractor: content => content.match(/[A-z0-9-_:/]+/g),
+  defaultExtractor: content => content.match(/[A-z0-9-_:/]+/g) || [],
 };
 
 module.exports = postcss.plugin('tailwind-purgecss', function(opts) {