PrimeFaces 12 dynamic file download return empty file

Question

I'm trying to use the p:fileDownload in my project to download csv files. I tried to use the example in the ShowCase but it didn't workd for me since the file is generated dynamic when the user clicks a button.

The logic is currently implemented in the getter-function but I also tried to place the logic in a separate function and pass the value to the variable. In both cases I received the file but the content was empty. If I debug I see that the data is available.

My Function

StreamedContent printDocFile;

//getter
public StreamedContent getPrintDocFile() {
    List<String> rows = //get information from DB

    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    OutputStreamWriter writer = new OutputStreamWriter(outputStream);
    CSVWriter csvWriter = new CSVWriter(writer);

    for (String row : rows) {
        String[] rowData = row.split(",");
        csvWriter.writeNext(rowData);
    }

    csvWriter.close();
                
    byte[] csvData = outputStream.toByteArray();
    ByteArrayInputStream stream = new ByteArrayInputStream(csvData);

    printDocFile = DefaultStreamedContent.builder()
                .name("test.csv")
                .contentType("text/csv")
                .stream(() -> stream)
                .build();
                
    stream.close();

    return printDocFile;
}

The button in the View

<p:commandButton id="downloadBtn" 
                 value="Print" 
                 update="form:msg">
    <p:fileDownload value="#{myController.printDocFile}"/>
</p:commandButton>

If I use the same code but instead p:fileDownload I use ExternalContext with ajax="false" the file has content.