code cleanup

core/common/iterator/src/main/java/org/eclipse/rdf4j/common/iteration/DualUnionIteration.java

@@ -63,13 +63,13 @@ public static <E> CloseableIteration<? extends E> getWildcardInstance(
 	public static <E> CloseableIteration<? extends E> getWildcardInstance(Comparator<E> cmp,
 			CloseableIteration<? extends E> leftIteration, CloseableIteration<? extends E> rightIteration) {
 
-//        if (rightIteration instanceof EmptyIteration) {
-//            return leftIteration;
-//        } else if (leftIteration instanceof EmptyIteration) {
-//            return rightIteration;
-//        } else {
-		return new DualUnionIteration<>(cmp, leftIteration, rightIteration);
-//        }
+		if (rightIteration instanceof EmptyIteration) {
+			return leftIteration;
+		} else if (leftIteration instanceof EmptyIteration) {
+			return rightIteration;
+		} else {
+			return new DualUnionIteration<>(cmp, leftIteration, rightIteration);
+		}
 	}
 
 	public static <E> CloseableIteration<E> getInstance(CloseableIteration<E> leftIteration,

core/common/iterator/src/main/java/org/eclipse/rdf4j/common/iteration/IndexReportingIterator.java

@@ -14,7 +14,7 @@
 import org.eclipse.rdf4j.common.annotation.Experimental;
 
 /**
- * The index name of the underlying data structure, e.g. SPOC, POSC, etc.
+ * A way to signal which index is in use for a specific iterator (e.g. SPOC, POSC, etc.). Used in the query explanation.
  */
 @Experimental
 public interface IndexReportingIterator {

core/common/order/src/main/java/org/eclipse/rdf4j/common/order/AvailableStatementOrder.java

@@ -18,9 +18,22 @@
 import org.eclipse.rdf4j.model.Resource;
 import org.eclipse.rdf4j.model.Value;
 
+/**
+ * An interface for {@link StatementOrder} implementations that can report which orders they support for a given
+ * subject, predicate, object and contexts.
+ */
 @Experimental
 public interface AvailableStatementOrder {
 
+	/**
+	 * Returns the supported orders for the given subject, predicate, object and contexts.
+	 *
+	 * @param subj
+	 * @param pred
+	 * @param obj
+	 * @param contexts
+	 * @return the supported orders for the given subject, predicate, object and contexts.
+	 */
 	@Experimental
 	Set<StatementOrder> getSupportedOrders(Resource subj, IRI pred, Value obj, Resource... contexts);
 }

core/common/order/src/main/java/org/eclipse/rdf4j/common/order/StatementOrder.java

@@ -17,13 +17,16 @@
 import org.eclipse.rdf4j.model.Statement;
 import org.eclipse.rdf4j.model.Value;
 
+/**
+ * An enum for the different orders in which statements can be ordered.
+ */
 @Experimental
 public enum StatementOrder {
 
-	S,
-	P,
-	O,
-	C;
+	S, // Subject
+	P, // Predicate
+	O, // Object
+	C; // Context
 
 	@Experimental
 	public Comparator<Statement> getComparator(Comparator<Value> comparator) {

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/QueryEvaluationContext.java

@@ -18,6 +18,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 
+import org.eclipse.rdf4j.common.annotation.Experimental;
 import org.eclipse.rdf4j.model.Literal;
 import org.eclipse.rdf4j.model.Value;
 import org.eclipse.rdf4j.model.ValueFactory;
@@ -36,7 +37,10 @@
  */
 public interface QueryEvaluationContext {
 
-	Comparator<Value> getComparator();
+	@Experimental
+	default Comparator<Value> getComparator() {
+		return null;
+	}
 
 	class Minimal implements QueryEvaluationContext {
 

core/queryalgebra/evaluation/src/test/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/GroupIteratorTest.java

@@ -64,7 +64,7 @@ public class GroupIteratorTest {
 	private final static ValueFactory vf = SimpleValueFactory.getInstance();
 	private static final EvaluationStrategy evaluator = new StrictEvaluationStrategy(null, null);
 	private static final QueryEvaluationContext context = new QueryEvaluationContext.Minimal(
-			vf.createLiteral(Date.from(Instant.now())), null);
+			vf.createLiteral(Date.from(Instant.now())), null, null);
 	private static BindingSetAssignment EMPTY_ASSIGNMENT;
 	private static BindingSetAssignment NONEMPTY_ASSIGNMENT;
 	private static AggregateFunctionFactory aggregateFunctionFactory;

core/queryalgebra/evaluation/src/test/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/JoinIteratorTest.java

@@ -59,7 +59,7 @@ public CloseableIteration<? extends Statement> getStatements(Resource subj, IRI
 		}
 	}, null);
 	private final QueryEvaluationContext context = new QueryEvaluationContext.Minimal(
-			vf.createLiteral(Date.from(Instant.now())), null);
+			vf.createLiteral(Date.from(Instant.now())), null, null);
 
 	/**
 	 * Tests joins between two different BindingSetAssignments with the same BindingSets but ordered differently.

core/queryalgebra/evaluation/src/test/java/org/eclipse/rdf4j/query/algebra/evaluation/util/OrderComparatorTest.java

@@ -47,9 +47,9 @@
 public class OrderComparatorTest {
 	private static final ValueFactory vf = SimpleValueFactory.getInstance();
 	private final QueryEvaluationContext context = new QueryEvaluationContext.Minimal(
-			vf.createLiteral(Date.from(Instant.now())), null);
+			vf.createLiteral(Date.from(Instant.now())), null, null);
 
-	class EvaluationStrategyStub implements EvaluationStrategy {
+	static class EvaluationStrategyStub implements EvaluationStrategy {
 
 		@Override
 		public CloseableIteration<BindingSet> evaluate(TupleExpr expr, BindingSet bindings)
@@ -69,19 +69,19 @@ public QueryEvaluationStep precompile(TupleExpr expr, QueryEvaluationContext con
 
 		@Override
 		public Value evaluate(ValueExpr expr, BindingSet bindings)
-				throws ValueExprEvaluationException, QueryEvaluationException {
+				throws QueryEvaluationException {
 			return null;
 		}
 
 		@Override
 		public boolean isTrue(ValueExpr expr, BindingSet bindings)
-				throws ValueExprEvaluationException, QueryEvaluationException {
+				throws QueryEvaluationException {
 			throw new UnsupportedOperationException();
 		}
 
 		@Override
 		public boolean isTrue(QueryValueEvaluationStep expr, BindingSet bindings)
-				throws ValueExprEvaluationException, QueryEvaluationException {
+				throws QueryEvaluationException {
 			throw new UnsupportedOperationException();
 		}