fixed inline thread replace error

lms/static/coffee/src/discussion/views/discussion_thread_show_view.coffee

@@ -125,7 +125,8 @@ class @DiscussionThreadShowView extends DiscussionContentView
         @model.set('endorsed', not endorsed)
 
   highlight: (el) ->
-    el.html(el.html().replace(/&lt;mark&gt;/g, "<mark>").replace(/&lt;\/mark&gt;/g, "</mark>"))
+    if el.html()
+      el.html(el.html().replace(/&lt;mark&gt;/g, "<mark>").replace(/&lt;\/mark&gt;/g, "</mark>"))
 
 class @DiscussionThreadInlineShowView extends DiscussionThreadShowView
   renderTemplate: ->

lms/templates/discussion/mustache/_inline_thread.mustache

@@ -6,10 +6,10 @@
             <h3>{{title}}</h3>
             <p class="posted-details">
                 {{#user}}
-                <a href="{{user_url}}" class="username">{{username}}</a>
+                    <a href="{{user_url}}" class="username">{{username}}</a>
                 {{/user}}
                 {{^user}}
-                anonymous
+                    anonymous
                 {{/user}}
 
                 <span class="timeago" title="{{created_at}}">{{created_at}}</span>