FIX: An opts hash was not, in fact, optional :)

lib/topic_retriever.rb

@@ -4,8 +4,8 @@ class TopicRetriever
 
   def initialize(embed_url, opts = nil)
     @embed_url = embed_url
-    @author_username = opts[:author_username]
     @opts = opts || {}
+    @author_username = @opts[:author_username]
   end
 
   def retrieve