Can't save to stream

[Frank Roelofs]

I am trying to merge several pdf documents from disk in an UWP app. I keep getting an execption when saving to the stream. (System.NullReferenceException: 'Object reference not set to an instance of an object.'). Why doesn't this work??? I can see that 

mergeDocument is valid and has the right pagecount etc.

    PdfDocument mergeDocument = new PdfDocument();

    foreach (StorageFile pdfFile in files)

    {

        PdfLoadedDocument loadedDocument = new PdfLoadedDocument();

        await loadedDocument.OpenAsync(pdfFile);

        PdfDocumentBase.Merge(mergeDocument, loadedDocument);

        loadedDocument.Close(true);

    }

     MemoryStream ms = new MemoryStream();

     await mergeDocument.SaveAsync(ms);

     mergeDocument.Close(true);

     Save(ms, "Samengevoegd.pdf");

Best regards,

Frank

[Frank Roelofs]

I discovered my mistake. Forgot this line:

     mergeDocument.EnableMemoryOptimization = true

Everything works fine now.

Best regards, Frank