Merge branch 'signout-rel-url' into 'master'

Use sign out path only if not empty

Fixes: https://github.com/gitlabhq/gitlabhq/issues/10066

See merge request !3989

app/controllers/application_controller.rb

@@ -117,7 +117,7 @@ def after_sign_in_path_for(resource)
   end
 
   def after_sign_out_path_for(resource)
-    current_application_settings.after_sign_out_path || new_user_session_path
+    current_application_settings.after_sign_out_path.presence || new_user_session_path
   end
 
   def abilities