3 files changed, 15 insertions, 6 deletions

diff --git a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java
index f5bd2efc..66dcb00f 100644
--- a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java
+++ b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationMode.java
@@ -21,6 +21,11 @@ public enum IntervalAggregationMode implements BinaryOperator<Interval> {
                                 }
                         };
                 }
+                
+                @Override
+                public Interval getNeutral() {
+                        return Interval.ZERO;
+                }
         },
 
         JOIN("intervalJoin", "Calculate the smallest interval containing all the intervals in a set") {
@@ -63,4 +68,8 @@ public enum IntervalAggregationMode implements BinaryOperator<Interval> {
         }
 
         public abstract IntervalRedBlackNode createNode(Interval interval);
+        
+        public Interval getNeutral() {
+                return Interval.EMPTY;
+        }
 }
diff --git a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend
index 940c71bb..21d3d73b 100644
--- a/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend
+++ b/Solvers/VIATRA-Solver/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/interval/IntervalAggregationOperator.xtend
@@ -36,13 +36,13 @@ class IntervalAggregationOperator implements IMultisetAggregationOperator<Interv
 
         override getAggregate(IntervalRedBlackNode result) {
                 if (result.leaf) {
-                        null
+                        mode.neutral
                 } else {
                         result.result
                 }
         }
 
         override aggregateStream(Stream<Interval> stream) {
-                stream.reduce(mode).orElse(null)
+                stream.reduce(mode).orElse(mode.neutral)
         }
 }
diff --git a/Tests/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra.tests/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/tests/interval/SumTest.xtend b/Tests/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra.tests/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/tests/interval/SumTest.xtend
index cbd7e71f..530c081c 100644
--- a/Tests/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra.tests/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/tests/interval/SumTest.xtend
+++ b/Tests/hu.bme.mit.inf.dslreasoner.viatrasolver.logic2viatra.tests/src/hu/bme/mit/inf/dslreasoner/viatrasolver/logic2viatra/tests/interval/SumTest.xtend
@@ -24,7 +24,7 @@ class SumTest {
 
         @Test
         def void emptyTest() {
-                assertEquals(null)
+                assertEquals(ZERO)
         }
 
         @Test
@@ -37,7 +37,7 @@ class SumTest {
         def void addRemoveTest() {
                 add(between(-1, 1))
                 remove(between(-1, 1))
-                assertEquals(null)
+                assertEquals(ZERO)
         }
 
         @Test
@@ -79,7 +79,7 @@ class SumTest {
                 remove(between(-1, 1))
                 remove(between(-1, 1))
                 remove(between(-1, 1))
-                assertEquals(null)
+                assertEquals(ZERO)
         }
 
         @Test
@@ -108,7 +108,7 @@ class SumTest {
                         } else {
                                 current.remove(interval)
                         }
-                        val expected = current.stream.reduce(aggregator.mode).orElse(null)
+                        val expected = current.stream.reduce(aggregator.mode).orElse(ZERO)
                         update(interval, isInsert)
                         assertEquals(expected)
                 }