code: private static <T, ET> boolean hasNullValueEdges(DataSet<Edge<T, ET>> edges) {
  		TypeInformation<?> genericTypeInfo = edges.getType();
  		@SuppressWarnings("unchecked")
  		TupleTypeInfo<Tuple3<T, T, ET>> tupleTypeInfo = (TupleTypeInfo<Tuple3<T, T, ET>>) genericTypeInfo;
  
  		return tupleTypeInfo.getTypeAt(2).equals(ValueTypeInfo.NULL_VALUE_TYPE_INFO);
  	}
docs: Check whether the edge type of the {@link DataSet} is {@link NullValue}.
  
  @param edges data set for introspection
  @param <T> graph ID type
  @param <ET> edge value type
  @return whether the edge type of the {@link DataSet} is {@link NullValue}