docs: public <K, EV> Graph<K, NullValue, EV> edgeTypes(Class<K> vertexKey, Class<EV> edgeValue) {
  
  		if (edgeReader == null) {
  			throw new RuntimeException("The edge input file cannot be null!");
  		}
  
  		DataSet<Tuple3<K, K, EV>> edges = edgeReader
  			.types(vertexKey, vertexKey, edgeValue)
  				.name(GraphCsvReader.class.getName());
  
  		return Graph.fromTupleDataSet(edges, executionContext);
  	}