NullPointerException while merging pdfs

I am getting a NullPointerException while merging pdfs.
I am using almost the same code as concat_pdf.java.  Code 
snippet follows the message. Any help would be greatly appreciated.

Jaideep


         Iterator it = _listOfPages.iterator();
         finalPDF = (String)it.next();

         while (it.hasNext()) {
            pageFile = (String)it.next();
            PdfReader reader = new PdfReader(pageFile);
            if (fileCount == 0) {
               document = new
com.lowagie.text.Document(reader.getPageSizeWithRotation(1));
               writer = new PdfCopy(document, new
FileOutputStream(finalPDF));
            }
            int pageCount = reader.getNumberOfPages();
            PdfImportedPage page;
            for (int i = 0; i < pageCount;) {
               ++i;
               page = writer.getImportedPage(reader, i);
               writer.addPage(page);
               System.out.println("Processed page " + i);
            }
            fileCount++;
         }


java.lang.NullPointerException
        at com.lowagie.text.pdf.PdfWriter.getPdfIndirectReference(Unknown
Source
)
        at com.lowagie.text.pdf.PdfImportedPage.<init>(Unknown Source)
        at com.lowagie.text.pdf.PdfReaderInstance.getImportedPage(Unknown
Source
)
        at com.lowagie.text.pdf.PdfCopy.getImportedPage(Unknown Source)




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