Fix nil error rendering activity

Author: fbacall

app/views/public_activity/common/_create.html.erb

@@ -3,7 +3,7 @@
 <%= t('activity.actions.create') %> <%= activity_resource(activity) %>
 <%= t('activity.timestamp', time: activity.created_at) -%>.
 <% source = activity.parameters[:source] %>
-<% if source && (current_user.is_admin? || current_user.is_curator?) %>
+<% if source && current_user && (current_user.is_admin? || current_user.is_curator?) %>
   <div class="sub-activity">
     <%= source[:id] ? link_to('Source', source_path(source[:id])) : '[sources.yml source]' %> -
     <%= source[:method] %> @