A question about dgl.nn.PyTorch.EGTLayer

I have a question about dgl.nn.PyTorch.EGTLayer. I don't know how to define the mask parameter in the forward function. According to the official documentation, I define the mask variable with the valid position set to 0 and the invalid position set to -inf. But my model weight always changes to Nan every time I execute the code. But that doesn't happen when I don't use the mask variable. So now I don't know how to define the mask variable. Can you give an example of using the mask variable? Thank you!