@Override
    public Optional<MessageCombiner<TraverserSet<Object>>> getMessageCombiner() {
        return (Optional) TraversalVertexProgramMessageCombiner.instance();
    }
Get the {@link PureTraversal} associated with the current instance of the {@link TraversalVertexProgram}.

@return the pure traversal of the instantiated program
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/traversal/TraversalVertexProgram.java