The gradient (Tensor.grad) of decoder weights is None

[NonvolatileMemory]

Hello,
I want to get the gradient w.r.t the parameters in decoder like embedding layer's weights and ffn layer's weights.
However when I run following command the results are always None.

print(model.decoder.layers[0].fc1.weight.grad)

and the following command always return True even the FFN weights:

model.decoder.layers[0].fc1.weight.is_leaf

I don't know where going wrong, thank you

[NonvolatileMemory]

hook works fine to get the gradient