diff --git a/activesupport/lib/active_support/core_ext/hash/conversions.rb b/activesupport/lib/active_support/core_ext/hash/conversions.rb
index 74e23bd884..a77fb55747 100644
--- a/activesupport/lib/active_support/core_ext/hash/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/hash/conversions.rb
@@ -9,7 +9,7 @@ class Object
   end
 
   def to_query(key) #:nodoc:
-    "#{key}=#{CGI.escape(to_param)}"
+    "#{key}=#{CGI.escape(to_param || "")}"
   end
 end