fix

vendor/built_in_modules/survey/app/controllers/panel/survey/back_end/surveys_controller.rb

@@ -108,7 +108,7 @@ class Panel::Survey::BackEnd::SurveysController < OrbitBackendController
                 end
               end.flatten
             else
-              ' '
+              [' ']
             end
           end
           max_length = csv_stats.map(&:length).max