Don't save unchanged user map items to the DB.

app/controllers/import/google_code_controller.rb

@@ -54,6 +54,11 @@ class Import::GoogleCodeController < Import::BaseController
       render "new_user_map" and return
     end
 
+    # This is the default, so let's not save it into the database.
+    user_map.reject! do |key, value|
+      value == Gitlab::GoogleCodeImport::Client.mask_email(key)
+    end
+
     session[:google_code_user_map] = user_map
 
     flash[:notice] = "The user map has been saved. Continue by selecting the projects you want to import."