For the parameters, the  grad_fn  will always be None

Is this is a reason that I get None for the last lines of code?
And another interesting thing I found out :
 large_lr_layers = nn.Sequential(*list(model.children())[:-4]).parameters()
 small_lr_layers = nn.Sequential(*list(model.children())[-4:]).parameters()
 for param in large_lr_layers:
     print(param)
 optimizer = optim.Adadelta([{"params": large_lr_layers,"lr":0.01},
                             {"params": small_lr_layers}],lr = args.lr)
 for param in large_lr_layers:
     print(param)

After setting the optimizer ,the second loop literally prints nothing? Why does this happen?