ray_indices, t_ends, t_starts are null(empty)

I use occestimator sampling, but t_start is null.

After a troubleshooting, I found that the sigma_fn function in occestimator.sampling is not executed, why is that? Can you help me?

this input of sampling, ray_d is normal, about ray_o, I assume it all starts  at (0,0,0), sigma_fn is normal, 