pdf417 Fail

[mynamecxy]

QZXing decoder;
if(codeType == BARCODE_TYPE_QRCODE)
{
    decoder.setDecoder( QZXing::DecoderFormat_QR_CODE );
}
else
{
    decoder.setDecoder( QZXing::DecoderFormat_PDF_417);
}

decoder.setSourceFilterType(QZXing::SourceFilter_ImageNormal);
decoder.setTryHarderBehaviour(QZXing::TryHarderBehaviour_ThoroughScanning | QZXing::TryHarderBehaviour_Rotate);

retMsg = decoder.decodeImage(imageToDecode);

heip:retMsg is NULL when I use QZXing::DecoderFormat_PDF_417!

QZXing version is 3.3.0; Qt version is 5.9.9 + VS2015 I tried, except PDF417,all ok!