Fix JS exception data callback

assets/javascripts/app/app.coffee

@@ -57,7 +57,8 @@
             mode: if @DOC then 'single' else 'full'
             iframe: (window.top isnt window).toString()
           dataCallback: (data) ->
-            try $.extend(data.user, app.settings.settings)
+            try $.extend(data.user ||= {}, app.settings.settings)
+            data
         .install()
       @previousErrorHandler = onerror
       window.onerror = @onWindowError.bind(@)