RuntimeError: cannot reshape tensor of 0 elements into shape [0, -1] because the unspecified dimension size -1 can be any value and is ambiguous

[YasminAkaichi]

I ran the basic file with no problem but the federated option didn't work, I got this error :
forward x = x.view(x.size(0), -1)
RuntimeError: cannot reshape tensor of 0 elements into shape [0, -1] because the unspecified dimension size -1 can be any value and is ambiguous