生成逗号分隔的字符串不起作用

[WebGet(UriTemplate = "csv")]
public Stream GetCollectionAsCsv()
{
    string[] myValues = { "test", "test","test" };
    string csvString = string.Join(",", myValues);

    byte[] csvBytes = Encoding.UTF8.GetBytes(csvString);


    if (WebOperationContext.Current != null)
    {
        WebOperationContext.Current.OutgoingResponse.ContentType = "text/csv";
        WebOperationContext.Current.OutgoingResponse.Headers["Content-Disposition"] = "attachment; filename=\"testss.csv\"";
    }


    return new MemoryStream(csvBytes);

}
[WebGet(UriTemplate = "csv")]
public Stream Get