fix thumbnail helper

app/helpers/learning_objects_helper.rb

@@ -4,9 +4,13 @@ module LearningObjectsHelper
     categories.to_s
   end
 
-  def learning_object_thumbnail(learning_object)
-    if learning_object.thumbnail == "thumbnai"
-      image_tag('learning-object-preview.png')
+  def learning_object_thumbnail(learning_object, size = "")
+    if learning_object.thumbnail.nil?
+      if size == "large"
+        image_tag('learning-object-preview-large.png')
+      else
+        image_tag('learning-object-preview.png')
+      end
     else
       image_tag learning_object.thumbnail, alt: learning_object_title(learning_object)
     end

app/views/learning_objects/show.html.erb

@@ -25,13 +25,7 @@
 
 <div class="row learning-object">
   <div class="col-md-7">
-    <%=
-      if (@learning_object.thumbnail == "thumbnai")
-        image_tag 'learning-object-preview-large.png', class: "thumbnail"
-      else
-        image_tag @learning_object.thumbnail, class: "thumbnail"
-      end
-    %>
+    <%= learning_object_thumbnail @learning_object, "large" %>
     <div class="stats">
       <span class="glyphicon glyphicon-eye-open"><%= @learning_object.views %>&nbsp;</span>
       <span class="glyphicon glyphicon-star"><%= @learning_object.likes %>&nbsp;</span>