Ensure we traverse the payloadJSON properly (#861)

Author: flovilmart

src/dashboard/Push/PushDetails.react.js

@@ -39,7 +39,7 @@ const EXP_STATS_URL = 'http://docs.parseplatform.org/ios/guide/#push-experiments
 let getMessage = (payload) => {
   if(payload) {
     let payloadJSON = JSON.parse(payload);
-		if (payloadJSON.alert.body) {
+		if (payloadJSON.alert && payloadJSON.alert.body) {
 			return payloadJSON.alert.body;
 		} else if (payloadJSON.alert) {
 			return payloadJSON.alert;