Merge pull request #250 from staticinstance/staticinstance-patch-248

patch for issue 248 (send null instead of undefined)

lib/adapters/xhr.js

@@ -125,6 +125,11 @@ 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);
 };