diff --git a/lib/summon/transport/headers.rb b/lib/summon/transport/headers.rb
index e08b3df..0dcf09c 100644
--- a/lib/summon/transport/headers.rb
+++ b/lib/summon/transport/headers.rb
@@ -43,7 +43,7 @@ def digest
     end
 
     def qstr
-      to_query_string(@params, false)
+      to_query_string(@params, false, lambda {|k,v| v.nil? })
     end
 
     private
diff --git a/lib/summon/transport/qstring.rb b/lib/summon/transport/qstring.rb
index dfbb413..b21e1f9 100644
--- a/lib/summon/transport/qstring.rb
+++ b/lib/summon/transport/qstring.rb
@@ -5,8 +5,9 @@
 module Summon::Transport
   module Qstring
 
-    def to_query_string(hash, urlencode = true)
-      hash.reject {|k,v| v.nil? || v == ''}.inject([]) do |qs,pair|
+    def to_query_string(hash, urlencode = true,
+			reject = lambda {|k,v| v.nil? || v == ''})
+      hash.reject(&reject).inject([]) do |qs,pair|
         qs.tap do
           k,v = pair
           if v.is_a?(Array)