fix can not guess problem

app/helpers/application_helper.rb

 require 'digest/md5'
 module ApplicationHelper
+  include Utils::CharEncode
   def gravatar_icon(user_email)
     gravatar_host = request.ssl? ? "https://secure.gravatar.com" :  "http://www.gravatar.com"

app/helpers/commits_helper.rb

 module CommitsHelper
-  include Utils::CharEncode
-
   def old_line_number(line, i)
   end

lib/utils.rb

@@ -18,13 +18,14 @@ module Utils
   module CharEncode
     def encode(string)
+      return '' unless string
       cd = CharDet.detect(string)
       if cd.confidence > 0.6
         string.force_encoding(cd.encoding)
       end
       string.encode("utf-8", :undef => :replace, :replace => "?", :invalid => :replace)
     rescue
-      "Invalid code encoding"
+      "Invalid Encoding"
     end
   end