link user avatar in activity page to user profile

app/views/events/_event.html.haml

@@ -4,7 +4,12 @@
       #{time_ago_with_tooltip(event.created_at)}
 
     = cache [event, current_application_settings, "v2.2"] do
-      = image_tag avatar_icon(event.author_email, 40), class: "avatar s40", alt:''
+      - if event.author
+        = link_to user_path(event.author.username) do
+          = image_tag avatar_icon(event.author_email, 40), class: "avatar s40", alt:''
+      - else
+        = image_tag avatar_icon(event.author_email, 40), class: "avatar s40", alt:''
+
       - if event.created_project?
         = render "events/event/created_project", event: event
       - elsif event.push?