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);
        }