iTextSharp creation of a pdf from a list of byte arrays

I've got a list of byte[] which i'd like to concatenate into one byte[] which will be the final PDf.

On the "page = copy.GetImportedPage(new PdfReader(p), i); " i'm getting an "object reference not set to an instance error.

I've got no clue of what's going on, i've already checked every object and there's no null.

Any ideas on this, or another piece of code that could make the trick?!

I've got this method:

EDIT

      public static byte[] concatAndAddContent(List<byte[]> pdf)
    {
        byte [] todos;

        using(MemoryStream ms = new MemoryStream())
        {
            Document doc = new Document();
            doc.Open();

            PdfCopy copy = new PdfCopy(doc, ms);
            PdfCopyFields copy2 = new PdfCopyFields(ms);


            PdfReader reader;
            foreach (byte[] p in pdf)
            {
                reader = new PdfReader(p);
                int pages = reader.NumberOfPages;

                // loop over document pages
                for (int i = 1; i < pages; i++)
                {
                    PdfImportedPage page = copy.GetImportedPage(reader, i);
                    PdfCopy.PageStamp stamp = copy.CreatePageStamp(page);
                    PdfContentByte cb = stamp.GetUnderContent();
                    cb.SaveState();
                    stamp.AlterContents();
                    copy.AddPage(page);
                }
            }

            doc.Close();
            todos = ms.GetBuffer();
            ms.Flush();
            ms.Dispose();
        }

        return todos;
    }

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   iTextSharp.text.pdf.PdfImportedPage..ctor(PdfReaderInstance readerInstance, PdfWriter writer, Int32 pageNumber) +45
   iTextSharp.text.pdf.PdfReaderInstance.GetImportedPage(Int32 pageNumber) +175
   iTextSharp.tex