Merge pull request #7981 from jfsiebel/fix-pop-up-clear-chat-problem

Fix problem with clear chat when popup alerts are enabled

bigbluebutton-html5/imports/ui/components/chat/alert/component.jsx

@@ -204,7 +204,7 @@ class ChatAlert extends PureComponent {
                 const reducedMessage = Service
                   .reduceAndMapGroupMessages(pendingNotificationsByChat[chatId].slice(-5)).pop();
 
-                if (!reducedMessage) return null;
+                if (!reducedMessage || !reducedMessage.sender) return null;
 
                 const content = this
                   .createMessage(reducedMessage.sender.name, reducedMessage.content);