Pytorch Geometric AssertionError

Hello everybody,
I’m learning to use PyTorch Geometric, I tried to replicate the WL kernel written by the PyG developers on GitHub (pytorch_geometric/wl_kernel.py at master · pyg-team/pytorch_geometric · GitHub), but when i run the program I get this error which I can’t solve:

Which one had the same problem and was able to solve it? Thank you all!