Return empty fragment if the entities are not found.

Author: RubenVerborgh

src/org/linkeddatafragments/datasource/BasicLinkedDataFragmentImpl.java renamed to src/org/linkeddatafragments/datasource/BasicLinkedDataFragmentBase.java

@@ -1,23 +1,31 @@
 package org.linkeddatafragments.datasource;
 
 import com.hp.hpl.jena.rdf.model.Model;
+import com.hp.hpl.jena.rdf.model.ModelFactory;
 
 /**
  * Base implementation of a Basic Linked Data Fragment.
  * @author Ruben Verborgh
  */
-public class BasicLinkedDataFragmentImpl implements BasicLinkedDataFragment {
+public class BasicLinkedDataFragmentBase implements BasicLinkedDataFragment {
 	private final Model triples;
 	private final long totalSize;
 
 	/**
-	 * Create a new Basic Linked Data Fragment.
+	 * Creates an empty Basic Linked Data Fragment.
+	 */
+	public BasicLinkedDataFragmentBase() {
+		this(null, 0);
+	}
+	
+	/**
+	 * Creates a new Basic Linked Data Fragment.
 	 * @param triples the triples (possibly partial)
 	 * @param totalSize the total size
 	 */
-	public BasicLinkedDataFragmentImpl(Model triples, long totalSize) {
-		this.triples = triples;
-		this.totalSize = totalSize;
+	public BasicLinkedDataFragmentBase(Model triples, long totalSize) {
+		this.triples = triples == null ? ModelFactory.createDefaultModel() : triples;
+		this.totalSize = totalSize < 0 ? 0 : totalSize;
 	}
 
 	@Override

src/org/linkeddatafragments/datasource/HdtDataSource.java

@@ -41,6 +41,8 @@ public BasicLinkedDataFragment getFragment(Resource subject, Property predicate,
         final int subjectId = subject == null ? 0 : dictionary.getIntID(subject.asNode(), TripleComponentRole.SUBJECT);
         final int predicateId = predicate == null ? 0 : dictionary.getIntID(predicate.asNode(), TripleComponentRole.PREDICATE);
         final int objectId = object == null ? 0 : dictionary.getIntID(object.asNode(), TripleComponentRole.OBJECT);
+        if (subjectId < 0 || predicateId < 0 || objectId < 0)
+        	return new BasicLinkedDataFragmentBase();
 		final IteratorTripleID result = datasource.getTriples().search(new TripleID(subjectId, predicateId, objectId));
 
 		// create the fragment