private static <T extends Traversal.Admin<Vertex, Edge>> T setVertexStart(final Traversal.Admin<Vertex, Edge> incidentTraversal, final Vertex vertex) {
        incidentTraversal.asAdmin().addStart(incidentTraversal.getTraverserGenerator().generate(vertex, incidentTraversal.asAdmin().getStartStep(), 1l));
        return (T) incidentTraversal;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
spark-gremlin/src/main/java/org/apache/tinkerpop/gremlin/spark/process/computer/SparkMessenger.java