RuntimeError: Tensors must have same number of dimensions: got 3 and 2

[sumorday]

hey,I try to use some other method like word2vec, xlnet and ERNIE.
but when I run the last part of code.(pytorch version),it failed.

    # Generate the output of the Discriminator for real and fake data.
    # First, we put together the output of the tranformer and the generator
    **disciminator_input = torch.cat([hidden_states, gen_rep], dim=1)**

RuntimeError: Tensors must have same number of dimensions: got 3 and 2

I checked the shape below
gen_rep.shape ---->torch.Size([64, 768])
hidden_states.shape ---->torch.Size([64, 64, 768])
torch.cat((gen_rep,hidden_states),dim=1)
if I run the bert model it can work, but when I try to use other NLP model like Xlnet and ERNIE. it seems the issue of dimension is existing. How can I do?