diff --git a/client/bbb-html5-client/public/js/models/whiteboard_paper.coffee b/client/bbb-html5-client/public/js/models/whiteboard_paper.coffee
index 70c7e72222d7af912c8edf374a92bed1ad33ed6a..5c75a166041e015c98d163f632ee68cb6ce5140d 100755
--- a/client/bbb-html5-client/public/js/models/whiteboard_paper.coffee
+++ b/client/bbb-html5-client/public/js/models/whiteboard_paper.coffee
@@ -139,7 +139,7 @@ define [
         @removeAllImagesFromPaper()
         @slides = slidesTmp
         @rebuild()
-        @showImageFromPaper(urlTmp.url)
+        @showImageFromPaper(urlTmp?.url)
         # drawings
         tmp = _.clone(@currentShapesDefinitions)
         @clearShapes()
@@ -871,7 +871,7 @@ define [
 
     # Adds the base url (the protocol+server part) to `url` if needed.
     _slideUrl: (url) ->
-      if url.match(/http[s]?:/)
+      if url?.match(/http[s]?:/)
         url
       else
         globals.presentationServer + url
diff --git a/client/bbb-html5-client/public/js/views/session_chat.coffee b/client/bbb-html5-client/public/js/views/session_chat.coffee
index 79decebcec7548fb1fac16ae77d94724e14d4094..c0817b9d8f194ca55c131ea09ec9d2fae402d000 100755
--- a/client/bbb-html5-client/public/js/views/session_chat.coffee
+++ b/client/bbb-html5-client/public/js/views/session_chat.coffee
@@ -57,8 +57,9 @@ define [
         @_scrollToBottom()
 
       globals.events.on "chat:all_messages", (messages) =>
-        for msgBlock in messages
-          @_addChatMessage(msgBlock.username, msgBlock.message)
+        if messages?
+          for msgBlock in messages
+            @_addChatMessage(msgBlock.username, msgBlock.message)
         @_scrollToBottom()
 
       globals.events.on "users:user_leave", (userid) =>