How write data in mem `Graph` using UpdateRequest?

[Eugene Tenkaev (Hronom)]

Hello everyone! 
I use Apache Jena version 2.13.0.
I try to add in existing Graph new triple by using SPARQL, and triple didn’t 
added, here is the code:
public class TestTransactions {
    public static void main(String[] args) {
        Dataset dataset = TDBFactory.createDataset();
        DatasetGraph datasetGraph = dataset.asDatasetGraph();
        Graph graph = datasetGraph.getDefaultGraph();

        // Fill graph.
        graph.add(
            new Triple(
                NodeFactory.createURI("http://example/unit13";),
                NodeFactory.createURI("http://example/name";),
                NodeFactory.createLiteral("Unit 13", "en")
            )
        );

        graph.add(
            new Triple(
                NodeFactory.createURI("http://example/unit13";),
                NodeFactory.createURI("http://example/type";),
                NodeFactory.createURI("http://example/robot";)
            )
        );

        graph.add(
            new Triple(
                NodeFactory.createURI("http://example/unit13";),
                NodeFactory.createURI("http://example/creationYear";),
                NodeFactory.createURI("http://example/2015";)
            )
        );

        // Test.
        dataset.begin(ReadWrite.WRITE);

        UpdateRequest request =
            UpdateFactory.create(
            "INSERT { ?s <http://example/value> '1' } WHERE { ?s 
<http://example/creationYear> <http://example/2015> . }"
        );
        UpdateAction.execute(request, dataset);

        dataset.commit();
        dataset.end();

        RDFDataMgr.write(System.out, graph, RDFFormat.NTRIPLES);
    }
}

If I remove “dataset.begin(ReadWrite.WRITE);”, “dataset.commit();” and 
“dataset.end();” triple will be inserted…

Test project on GitHub https://github.com/Hronom/test-jena