code: public FaunusPipeline V() {
          this.state.assertNotLocked();
          this.state.assertNoProperty();
          this.state.set(Vertex.class);
  
          this.compiler.addMap(VerticesMap.Map.class,
                  NullWritable.class,
                  FaunusVertex.class,
                  VerticesMap.createConfiguration(this.state.incrStep() != 0));
  
          makeMapReduceString(VerticesMap.class);
          return this;
      }
docs: Start a traversal at all vertices in the graph.
  
  @return the extended FaunusPipeline