user.save missing variable

The user.save service is missing a variable. At the moment only the variable uid is required. There should be a second variable, containing the fields (name, mail, pass, etc.). Trying the user.save service 'out of the box' does not work for me, when I use the following code, it does:

function user_service_save($account, $user) {

 if (!$account = user_save($account, $user)) {
    return services_error(t('Error on saving the user.'));
  }


  // Everything went right.
  // Return the user ID
  return $account->uid;
}