code: public static <K, EV> DataSet<Vertex<K, NullValue>> vertexSet(DataSet<Edge<K, EV>> edges, int parallelism) {
  		DataSet<Vertex<K, NullValue>> vertexSet = edges
  			.flatMap(new EmitSrcAndTarget<>())
  				.setParallelism(parallelism)
  				.name("Emit source and target labels");
  
  		return vertexSet
  			.distinct()
  			.setCombineHint(CombineHint.HASH)
  				.setParallelism(parallelism)
  				.name("Emit vertex labels");
  	}
docs: Generates {@link Vertex vertices} present in the given set of {@link Edge}s.
  
  @param edges source {@link DataSet} of {@link Edge}s
  @param parallelism operator parallelism
  @param <K> label type
  @param <EV> edge value type
  @return {@link DataSet} of discovered {@link Vertex vertices}
  
  @see Graph#fromDataSet(DataSet, DataSet, ExecutionEnvironment)