System.Text.UnicodeEncoding.GetPreamble C# (CSharp) Method

        public override byte[] GetPreamble()
        {
            throw null;
        }

 private void DoExportForHishop(string csvFilename, string imagePath, System.Collections.Generic.List <ExportToLocal.ProductDetail> list)
 {
     using (System.IO.FileStream fileStream = new System.IO.FileStream(csvFilename, System.IO.FileMode.Create, System.IO.FileAccess.Write))
     {
         string productCSVForEcdev = this.GetProductCSVForHishop(imagePath, list);
         System.Text.UnicodeEncoding unicodeEncoding = new System.Text.UnicodeEncoding();
         //UTF8Encoding unicodeEncoding = new UTF8Encoding();
         int    byteCount = unicodeEncoding.GetByteCount(productCSVForEcdev);
         byte[] preamble  = unicodeEncoding.GetPreamble();
         byte[] array     = new byte[preamble.Length + byteCount];
         System.Buffer.BlockCopy(preamble, 0, array, 0, preamble.Length);
         unicodeEncoding.GetBytes(productCSVForEcdev.ToCharArray(), 0, productCSVForEcdev.Length, array, preamble.Length);
         fileStream.Write(array, 0, array.Length);
     }
     using (ZipFile zipFile = new ZipFile(System.Text.Encoding.Default))
     {
         System.IO.DirectoryInfo directoryInfo = new System.IO.DirectoryInfo(imagePath);
         zipFile.CompressionLevel = CompressionLevel.Default;
         zipFile.AddFile(csvFilename, "");
         zipFile.AddDirectory(directoryInfo.FullName, directoryInfo.Name);
         System.Web.HttpResponse response = System.Web.HttpContext.Current.Response;
         response.ContentType     = "application/x-zip-compressed";
         response.ContentEncoding = this._encoding;
         response.AddHeader("Content-Disposition", "attachment; filename=" + directoryInfo.Name + ".zip");
         response.Clear();
         zipFile.Save(response.OutputStream);
         this._workDir.Delete(true);
         response.Flush();
         response.Close();
     }
 }