How would you handle sparql xml directly when QueryWithResultSet is not working

Question

How would you handle sparql xml directly when QueryWithResultSet is not working

Over the past year or so, I have used a bunch of custom code to interact with multiple endpoints SPARQL. I would rather not support it, so I learned how to use it dotnetrdf. The problem I have is that I encounter endpoints that I cannot work with. Here is an example: Endpoint http://id.ndl.go.jp/auth/ndla SPARQL Query::

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 
PREFIX xl: <http://www.w3.org/2008/05/skos-xl#>
SELECT ?subj WHERE { 
{?subj rdfs:label ?heading} UNION
{?subj xl:altLabel [ xl:literalForm ?heading]}
filter (?heading = "軍事基地.")
}

If you run this query as a query GET, it works:SPARQL QUERY

The problem with this dotnetrefis that I am trying to do the following:

SparqlRemoteEndpoint endpoint = new SparqlRemoteEndpoint(new Uri(@"http://id.ndl.go.jp/auth/ndla"));
endpoint.HttpMode = "GET";               
SparqlResultSet results = endpoint.QueryWithResultSet(textBox1.Text);

POST - , HTML. , :

System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(@"http://id.ndl.go.jp/auth/ndla?query=PREFIX%20rdfs%3A%20%3Chttp%3A%2F%2Fwww.w3.org%2F2000%2F01%2Frdf-schema%23%3E%20%0APREFIX%20xl%3A%20%3Chttp%3A%2F%2Fwww.w3.org%2F2008%2F05%2Fskos-xl%23%3E%0ASELECT%20%3Fsubj%20WHERE%20%7B%20%0A%20%7B%3Fsubj%20rdfs%3Alabel%20%3Fheading%7D%20UNION%0A%20%7B%3Fsubj%20xl%3AaltLabel%20%5B%20xl%3AliteralForm%20%3Fheading%5D%7D%0A%20filter%20(%3Fheading%20%3D%20%22%E8%BB%8D%E4%BA%8B%E5%9F%BA%E5%9C%B0%22)%0A%20%7D");

System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)request.GetResponse();           
System.IO.Stream s = response.GetResponseStream();
System.IO.StreamReader reader = new System.IO.StreamReader(s);
string _s = reader.ReadToEnd();
reader.Close();
s.Close();

raw sparql xml, , dotnetrdf. , .