temporary fix for learning objects helper

app/helpers/learning_objects_helper.rb

@@ -5,7 +5,7 @@ module LearningObjectsHelper
   end
 
   def learning_object_thumbnail(learning_object, size = "")
-    if learning_object.thumbnail.nil?
+    if learning_object.thumbnail.nil? || learning_object.thumbnail == "thumbnai" # TODO: remove "thumbnai" when possible
       if size == "large"
         image_tag('learning-object-preview-large.png')
       else