@Override
    public <S, C> List<Traversal.Admin<S, C>> getLocalChildren() {
        final List<Traversal.Admin<S, C>> children = super.getLocalChildren();
        if (outVTraversal != null) children.add((Traversal.Admin<S, C>) outVTraversal);
        if (inVTraversal != null) children.add((Traversal.Admin<S, C>) inVTraversal);
        return children;
    }
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