P2F metric return Nan

[rhtm02]

First of all, thank you so much for the code
I have a problem using the code, so I'm asking you a question.
In the evaluation_code, the p2f value between my output point cloud and ground truth point cloud is Nan.
I took a print and found that pred_map_points[i] = shortest_paths.point(location.first,location.second); was Nan. I wonder if you've ever experienced this before. Also, what should I do if I had one?