Merge branch 'issue_15390' into 'master'

Fix javascript errors with invalid json because of commas

fixes #15390 

See merge request !3827

app/views/shared/issuable/_sidebar.html.haml

@@ -151,6 +151,6 @@
     :javascript
       new MilestoneSelect('{"namespace":"#{@project.namespace.path}","path":"#{@project.path}"}');
       new LabelsSelect();
-      new IssuableContext('#{current_user.to_json(only: [:username, :id, :name])}');
+      new IssuableContext('#{escape_javascript(current_user.to_json(only: [:username, :id, :name]))}');
       new Subscription('.subscription')
       new Sidebar();