code: public FaunusPipeline path() {
          this.state.assertNotLocked();
          this.state.assertNoProperty();
  
          this.compiler.addMap(PathMap.Map.class,
                  NullWritable.class,
                  Text.class,
                  PathMap.createConfiguration(this.state.getElementType()));
          this.state.lock();
          makeMapReduceString(PathMap.class);
          return this;
      }
docs: Emit the path taken from start to current element.
  
  @return the extended FaunusPipeline