Make sure headers object exists

src/index.js

@@ -11,6 +11,7 @@ http.createServer((req, res) => {
 
 	const handleResponse = origRes => {
 		res.statusCode = origRes.statusCode;
+		origRes.headers = origRes.headers || {};
 		Object.entries(origRes.headers).forEach(header => {
 			if (header[0] !== 'content-encoding') {
 				res.setHeader(header[0], header[1]);