do not publish undefined poll

bigbluebutton-html5/imports/api/polls/server/methods/publishPoll.js

 import RedisPubSub from '/imports/startup/server/redis';
 import { check } from 'meteor/check';
 import Polls from '/imports/api/polls';
+import Logger from '/imports/startup/server/logger';
 
 export default function publishPoll(credentials) {
   const { meetingId, requesterUserId } = credentials;
@@ -12,13 +13,16 @@ export default function publishPoll(credentials) {
   check(requesterUserId, String);
 
   const poll = Polls.findOne({ meetingId });
-  const requester = requesterUserId;
+  if (!poll) {
+    Logger.error(`Attempted to publish inexisting poll for meetingId: ${meetingId}`);
+    return false;
+  }
 
   return RedisPubSub.publishUserMessage(
     CHANNEL,
     EVENT_NAME,
     meetingId,
-    requester,
+    requesterUserId,
     ({ requesterId: requesterUserId, pollId: poll.id }),
   );
 }