Integrate with #355

Author: gpoitch

lib/middleware.js

@@ -73,9 +73,9 @@ module.exports = function wrapper(context) {
         let contentType = mime.getType(filename) || '';
         const mimeInfo = mimeDb[contentType];
         const charset = (mimeInfo && mimeInfo.charset)
-          // Special-cased text/html to prevent possible breaking change.
+          // Special-cased text/html & empty to prevent possible breaking change.
           // TODO: remove the following line in next major release.
-          || (contentType === 'text/html' && 'UTF-8');
+          || ((contentType === 'text/html' || !contentType) && 'UTF-8');
 
         if (charset) {
           contentType += `; charset=${charset}`;