method PdfCopy.fixTaggedStructure throws NullPointerException

I am merging tagged pdf with untagged pdf. I am getting exception when I close Document object:
    NullPointerException(PdfCopy.java:890)

    Call stack
    com.itextpdf.text.pdf.PdfCopy.fixTaggedStructure(PdfCopy.java:890)
    com.itextpdf.text.pdf.PdfCopy.flushTaggedObjects(PdfCopy.java:866)
    com.itextpdf.text.pdf.PdfDocument.close(PdfDocument.java:855)
    com.itextpdf.text.Document.close(Document.java:416)
    ......

Code:
        PdfReader basePDF = new PdfReader( byteArray );
        PdfReader legendInformation = new PdfReader( legendsStaticPDFs.get( language ) );

        boolean isBasePDFTagged = basePDF.isTagged();
        boolean islegendInformationTagged = legendInformation.isTagged();

        // Representation of the resultant, merged, PDF
        Document document = new Document( basePDF.getPageSize( 1 ) );

        // Wrap the target PDF in something concrete to facilitate adding pages
        ByteArrayOutputStream outputStreamNew = new ByteArrayOutputStream();
        PdfCopy newPDF = new PdfCopy( document, outputStreamNew );
        newPDF.setTagged();
        // Set the PDF language (Accessibility standards)
        newPDF.getExtraCatalog().put(PdfName.LANG,
            new PdfString( language.locale.getLanguage() ) );

        // Set the PDF document title (Accessibility standards)
        newPDF.getInfo().put(PdfName.TITLE, new PdfString(
                messageSourceAccessor.getMessage(
                        "statement.pdf.title." + language.locale.getLanguage() ) ) );

        document.open();
        appendPDF( newPDF, basePDF );
        //appendPDF( newPDF, legendInformation );
        document.close();

I checked this Merging Tagged PDF without ruining the tags<http://stackoverflow.com/questions/19839445/merging-tagged-pdf-without-ruining-the-tags>, and have found that it should be fixed, but it still exist at least in iText 5.5.2 I used. Is it any work around? Could PageName.PG be set manually? Thanks in advance.

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