FIX: Missing "no activity" message.

app/assets/javascripts/discourse/routes/user-activity-stream.js.es6

@@ -6,7 +6,10 @@ export default Discourse.Route.extend(ViewingActionType, {
   },
 
   afterModel() {
-    return this.modelFor("user").get("stream").filterBy(this.get("userActionType"), this.get("noContentHelpKey"));
+    return this.modelFor("user").get("stream").filterBy(
+      this.get("userActionType"),
+      this.get("noContentHelpKey") || "user_activity.no_default"
+    );
   },
 
   renderTemplate() {

config/locales/server.en.yml

@@ -708,6 +708,9 @@ en:
       long_form: 'voted for this post'
 
   user_activity:
+    no_default:
+      self: "You have no activity yet."
+      others: "No activity."
     no_bookmarks:
       self: "You have no bookmarked posts, bookmarking posts allows you to easily access them later on."
       others: "No bookmarks."