public async Task <Guid> SendFileAsync(Stream document, string filename, string destinationFolder)
{
var url = FileMetadata.AsQueryStringUrl("documents", filename, destinationFolder);
var content = new StreamContent(document);
var response = await _client.PostAsync(url, content);
var documentResponse = await response.Content.ReadAsAsync <DocumentResponse>();
return(documentResponse?.document_guid ?? Guid.Empty);
}