function rules_action_mail_to_user_upgrade in Rules 7.2
File
- includes/rules.upgrade.inc, line 621 
- Contains code for upgrading rule configurations from 6.x-1.x to 7.x-2.x.
Code
function rules_action_mail_to_user_upgrade($element, $target) {
  $target->settings['to:select'] = $element['#settings']['#argument map']['user'] . ':mail';
}