Only show the preloaded messages for activities that makes sense

app/views/activities/index.json.jbuilder

@@ -1,6 +1,12 @@
 json.array!(@activities) do |activity|
   activity = activity.decorate
-  json.extract! activity, :id, :type, :activity_message, :reciprocate_message, :acknowledge_message
+  json.extract! activity, :id, :type, :activity_message
+
+  if activity.type == 'received'
+    json.reciprocate_message = activity.reciprocate_message
+    json.acknowledge_message = activity.acknowledge_message
+  end
+
   json.message do
     # Sadly, this step is needed because extract doesn't find the at_in_words methods from the decorator.
     json.extract! activity.message, :id, :verb, :sender, :recipient, :acknowledged_at, :acknowledged_at_in_words, :created_at, :created_at_in_words