code: public FaunusPipeline _() {
          this.state.assertNotLocked();
          this.compiler.addMap(IdentityMap.Map.class,
                  NullWritable.class,
                  FaunusVertex.class,
                  IdentityMap.createConfiguration());
          makeMapReduceString(IdentityMap.class);
          return this;
      }
docs: The identity step does not alter the graph in anyway.
  It has the benefit of emitting various useful graph statistic counters.
  
  @return the extended FaunusPipeline