GAN implementation - v1 / v2 difference

I was going through the code of GAN impelentation to compare v2 and v1 to see if there are any differences. I noticed that v1 zeros gradients after the batch ( 127line) in GANTrainer

def on_batch_end(self, **kwargs):

while I can’t see zeroing gradients in v2 at any point. What is the reason for that or am I overlooking something?