https://github.com/cybertronai/pytorch-sso/blob/d16173236728fdd1e943bc3b61243bfb28f95348/torchsso/optim/vi.py#L200C31-L200C31
From the above line, if closure is None, an error would be occurred as None is not callable.
So, it looks like closure cannot be None in step.
What do you think about that?