Fix for https://github.com/mzabriskie/axios/issues/248

undefined is not valid JSON, make the value null instead.

JSON.parse(undefined) will throw an exception while JSON.parse(null) is acceptable.

http://stackoverflow.com/a/14946821/5012948

lib/adapters/xhr.js

@@ -125,6 +125,9 @@ module.exports = function xhrAdapter(resolve, reject, config) {
     requestData = new DataView(requestData);
   }
 
+  // Clean up request
+  requestData = requestData === undefined ? null : requestData;
+  
   // Send the request
   request.send(requestData);
 };