注意：iconv（）：检测到输入字符串中的非法字符。 Pdf捆绑

ContextErrorException: Notice: iconv(): Detected an illegal character in input string in /var/www/adwords-up/vendor/zendframework/zendpdf/library/ZendPdf/Resource/Font/Simple/AbstractSimple.php line 253

I have this error with non english symbols. Symfony 2.3, PdfBundle.

How i can fix this problem? Thanks.

    $total_string=NumToString::num2str($total);
    $facade = $this->get('ps_pdf.facade');
    $xml = $this->renderView('@AdwordsupClient/Billing/expense.pdf.twig',[
        'total_string'=>$total_string]);
    $content = $facade->render($xml);
    return new Response($content, 200, array('content-type' => 'application/pdf; charset=utf-8'));