fix the NullPointerException issue. for issue detail please check htt…

[Xiaoshu-Zhao]

fix the NullPointerException issue. for issue detail please check #637

[angelozerr]

Thanks @Xiaoshu-Zhao !

[Adrian012344]

I am having the same problem when trying to convert an Apache POI document to PDF with the method:

private byte[] createPdf(XWPFDocument document) {
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    PdfOptions options = PdfOptions.create();
    document.enforceReadonlyProtection();
    try {
        PdfConverter.getInstance().convert(document, byteArrayOutputStream, options);
    } catch (IOException e) {
        throw new RuntimeException("Pdf converter failed", e);
    }
    return byteArrayOutputStream.toByteArray();
}.

Will this fix also work for PDFs? And will this fix be released soon?
Have a good day.