fix

vendor/built_in_modules/survey/app/models/survey.rb

@@ -43,7 +43,7 @@ class Survey
 
   def time_range
     r = "#{self.postdate.to_date}"
-    r += "- #{self.deadline.to_date}" if self.deadline
+    r += "- #{self.deadline.to_date}" unless self.deadline.nil?
     r
   end