fix: return string array

js/src/forum/components/Post.js

@@ -132,7 +132,7 @@ export default class Post extends Component {
       'Post--loading': this.loading,
       'Post--by-actor': user === app.session.user,
       'Post--by-start-user': user?.id() === discussion.attribute('startUserId'),
-    });
+    }).split(' ').filter(x => !!x);
   }
 
   /**