Calling #to_s on a field with a nil value returns an empty string ins…

…tead of nil

Fixes #194

CHANGELOG.rdoc

@@ -11,6 +11,7 @@ Performance:
 * Close pull request 488 - Speed up field construction & comparison (bpot)
 
 Bugs:
+* Calling #to_s on a field with a nil value returns an empty string instead of nil (jeremy)
 * The Received header may contain zero name/value pairs, qmail-style (jeremy)
 * Fix that setting an attachment with a :mime_type and :encoding would override the :encoding (jeremy)
 * Fix that declaring an html_part but no text_part would use multipart/alternative anyway (jeremy)

lib/mail/fields/common/common_field.rb

@@ -22,7 +22,7 @@ def value
     end
 
     def to_s
-      decoded
+      decoded.to_s
     end
 
     def default

spec/mail/fields/unstructured_field_spec.rb

@@ -43,7 +43,7 @@
 
     it "should return '' on to_s if there is no value" do
       @field.value = nil
-      @field.encoded.should eq ''
+      @field.to_s.should eq ''
     end
 
     it "should give an encoded value ready to insert into an email" do