@Override
    public void reset() {
        super.reset();
        if (outVTraversal != null) outVTraversal.reset();
        if (inVTraversal != null) inVTraversal.reset();
    }
Gets the traversal that will be used to provide the {@code Map} that will be used to identify the Direction.IN
vertex during merge.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MergeEdgeStep.java