public function retrieveUser ($username) {
        $query = $this->newUserQuery($username);
        try {
            $user = $this->getUserEntry($query);
        } catch (Zend_Gdata_Gapps_ServiceException $e) {
            // Set the user to null if not found
            if ($e->hasError(Zend_Gdata_Gapps_Error::ENTITY_DOES_NOT_EXIST)) {
                $user = null;
            } else {
                throw $e;
            }
        }
        return $user;
    }