Add null checks for inverse index related methods

Co-Authored-By: Max Kießling <max.kiessling@neotechnology.com>

Author: s1ck

core/src/main/java/org/neo4j/gds/core/huge/NodeFilteredGraph.java

@@ -147,6 +147,7 @@ public int degreeWithoutParallelRelationships(long nodeId) {
 
     @Override
     public int degreeInverse(long nodeId) {
+        validateIndexInverse();
         int cachedDegree = this.degreeInverseCache.get(nodeId);
         if (cachedDegree != NO_DEGREE) {
             return cachedDegree;
@@ -253,6 +254,7 @@ public void forEachRelationship(long nodeId, double fallbackValue, RelationshipW
 
     @Override
     public void forEachInverseRelationship(long nodeId, RelationshipConsumer consumer) {
+        validateIndexInverse();
         super.forEachInverseRelationship(
             filteredIdMap.toRootNodeId(nodeId),
             (s, t) -> filterAndConsume(s, t, consumer)
@@ -265,6 +267,7 @@ public void forEachInverseRelationship(
         double fallbackValue,
         RelationshipWithPropertyConsumer consumer
     ) {
+        validateIndexInverse();
         super.forEachInverseRelationship(
             filteredIdMap.toRootNodeId(nodeId),
             fallbackValue,
@@ -363,6 +366,14 @@ public NodePropertyValues nodeProperties(String propertyKey) {
         return new FilteredNodePropertyValues.FilteredToOriginalNodePropertyValues(properties, this);
     }
 
+    private void validateIndexInverse() {
+        if (this.degreeInverseCache == null) {
+            throw new UnsupportedOperationException(
+                "Cannot access inverse relationships as this graph is not inverse indexed."
+            );
+        }
+    }
+
     private boolean filterAndConsume(long source, long target, RelationshipConsumer consumer) {
         if (filteredIdMap.containsRootNodeId(source) && filteredIdMap.containsRootNodeId(target)) {
             long internalSourceId = filteredIdMap.toFilteredNodeId(source);

core/src/test/java/org/neo4j/gds/core/huge/NodeFilteredGraphTest.java

@@ -39,6 +39,7 @@
 import java.util.function.Function;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 @GdlExtension
@@ -83,7 +84,8 @@ void filteredIdMapThatIncludesAllNodes() {
         unfilteredGraph.forEachNode(nodeId -> {
             long filteredNodeId = filteredGraph.toFilteredNodeId(nodeId);
             if (unfilteredGraph.hasLabel(nodeId, filterLabel)) {
-                assertThat(filteredGraph.toOriginalNodeId(filteredNodeId)).isEqualTo(unfilteredGraph.toOriginalNodeId(nodeId));
+                assertThat(filteredGraph.toOriginalNodeId(filteredNodeId))
+                    .isEqualTo(unfilteredGraph.toOriginalNodeId(nodeId));
             } else {
                 assertThat(filteredNodeId).isEqualTo(IdMap.NOT_FOUND);
             }
@@ -230,6 +232,24 @@ void shouldStreamRelationshipsCorrectly() {
 
     }
 
+    @Test
+    void throwDegreeInverseIfNotIndexed() {
+        var graph = GdlFactory.of("(a:A)-->(b:B)-->(:B)").build().getGraph(NodeLabel.of("B"));
+
+        assertThatThrownBy(() -> graph.degreeInverse(0))
+            .isInstanceOf(UnsupportedOperationException.class)
+            .hasMessageContaining("Cannot access inverse relationships as this graph is not inverse indexed.");
+    }
+
+    @Test
+    void throwForeachInverseRelationshipIfNotIndexed() {
+        var graph = GdlFactory.of("(a:A)-->(b:B)-->(:B)").build().getGraph(NodeLabel.of("B"));
+
+        assertThatThrownBy(() -> graph.forEachInverseRelationship(0, (sourceNodeId, targetNodeId) -> true))
+            .isInstanceOf(UnsupportedOperationException.class)
+            .hasMessageContaining("Cannot access inverse relationships as this graph is not inverse indexed.");
+    }
+
     Function<String, Long> filteredIdFunction(Graph graph) {
         return (variable) -> graph.toMappedNodeId(idFunction.of(variable));
     }