When the email address is empty gitlab will give a 500 error

Since some conversion tools do commits with an empty commiters email
address gitlab will fail with a 500 error

app/helpers/application_helper.rb

@@ -3,6 +3,7 @@ module ApplicationHelper
 
   def gravatar_icon(user_email, size = 40)
     gravatar_host = request.ssl? ? "https://secure.gravatar.com" :  "http://www.gravatar.com"
+    user_email ||= ''
     user_email.strip!
     "#{gravatar_host}/avatar/#{Digest::MD5.hexdigest(user_email.downcase)}?s=#{size}&d=identicon"
   end