Issue #754: Fix serialisation of language tag in toSPARQL.

Signed-off-by: Joseph Walton <joe@kafsemo.org>

Author: josephw

core/queryrender/src/main/java/org/eclipse/rdf4j/queryrender/RenderUtils.java

@@ -78,7 +78,7 @@ else if (value instanceof Literal) {
 			builder.append("\"\"\"").append(escape(aLit.getLabel())).append("\"\"\"");
 
 			if (Literals.isLanguageLiteral(aLit)) {
-				builder.append("@").append(aLit.getLanguage());
+				aLit.getLanguage().ifPresent(lang -> builder.append("@").append(lang));
 			}
 			else {
 				builder.append("^^<").append(aLit.getDatatype().toString()).append(">");

core/queryrender/src/test/java/org/eclipse/rdf4j/queryrender/RenderUtilsTest.java

@@ -0,0 +1,26 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Eclipse RDF4J contributors.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Distribution License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *******************************************************************************/
+
+package org.eclipse.rdf4j.queryrender;
+
+import static org.junit.Assert.assertEquals;
+
+import org.eclipse.rdf4j.model.Value;
+import org.eclipse.rdf4j.model.impl.SimpleValueFactory;
+import org.junit.Test;
+
+public class RenderUtilsTest
+{
+    @Test
+    public void toSparqlWithLiteralSerialisesLanguageTag()
+    {
+        Value val = SimpleValueFactory.getInstance().createLiteral("test", "en");
+
+        assertEquals("\"\"\"test\"\"\"@en", RenderUtils.toSPARQL(val));
+    }
+}