public void Repro12901()
{
var graph = new BidirectionalGraph <int, Edge <int> >();
int vertex = 1;
graph.AddVerticesAndEdge(new Edge <int>(vertex, vertex));
var pathFinder = AlgorithmExtensions.ShortestPathsBellmanFord <int, Edge <int> >(graph, edge => - 1.0, vertex);
IEnumerable <Edge <int> > path;
pathFinder(vertex, out path);
}