Fix displaying events for deleted things

app/helpers/events_helper.rb

 module EventsHelper
   def link_to_author(event)
     project = event.project
-    tm = project.team_member_by_id(event.author_id)
+    tm = project.team_member_by_id(event.author_id) if project
 
     if tm
       link_to event.author_name, project_team_member_path(project, tm)

app/views/events/event/_common.html.haml

 .event-title
   %span.author_name= link_to_author event
   %span.event_label{class: event.action_name}= event_action_name(event)
-  = link_to [event.project, event.target] do
+  - if event.target
+    = link_to [event.project, event.target] do
+      %strong= truncate event.target_title
+  - else
     %strong= truncate event.target_title
   at
-  = link_to_project event.project
+  - if event.project
+    = link_to_project event.project
+  - else
+    = event.project_name