function getUserStrFIO($userId) {
    $userId = intval($userId);
    if ($userId <= 0) return null;

    $rsUser = CUser::GetByID($userId);
    $arUser = $rsUser->Fetch();

    if (!$arUser) return null;

    $parts = [];
    if (!empty($arUser["LAST_NAME"])) $parts[] = $arUser["LAST_NAME"];
    if (!empty($arUser["NAME"])) $parts[] = $arUser["NAME"];
    if (!empty($arUser["SECOND_NAME"])) $parts[] = $arUser["SECOND_NAME"];

    return empty($parts) ? null : implode(" ", $parts);
}