@Override
    protected Traverser.Admin<Vertex> processNextStart() {
        if (this.first) {
            this.first = false;
            final TraverserGenerator generator = this.getTraversal().getTraverserGenerator();
            final Vertex vertex = this.getTraversal().getGraph().get().addVertex(this.parameters.getKeyValues(generator.generate(false, (Step) this, 1L)));
            EventUtil.registerVertexCreation(callbackRegistry, getTraversal(), vertex);
            return generator.generate(vertex, this, 1L);
        } else
            throw FastNoSuchElementException.instance();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/AddVertexStartStep.java