Add getter to make parameterItems available for vendor implementations
diff --git a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/CombineStep.java b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/CombineStep.java
index ae854eb..ccf601a 100644
--- a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/CombineStep.java
+++ b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/CombineStep.java
@@ -68,6 +68,10 @@
         return (null == valueTraversal) ? Collections.emptyList() : Collections.singletonList(valueTraversal);
     }
 
+    public Object getParameterItems() {
+        return parameterItems;
+    }
+
     @Override
     public Set<TraverserRequirement> getRequirements() { return this.getSelfAndChildRequirements(); }