.NET C# HttpClient null bytes

using (HttpClient client = new HttpClient()) {
    StringContent sc = new StringContent(string.Empty);
    Task<HttpResponseMessage> resultTask = client.PostAsync(Server + "/p03c-ws/ovf2/" + SessionId, sc);
    resultTask.Wait(HttpTimeoutMs);
    using (HttpResponseMessage resp = resultTask.Result)
    using (HttpContent cnt = resp.Content) {
        return new HibakodokLista(DecodeDataXML<Ovf2.ovfHibakodok>(cnt.ReadAsStreamAsync().Result)).HIBAKODOK;
    }
}