I've looked at the code and in layers/convolution.py line 156:
dA[i, :, :, :] = da_pad[pad_h: -pad_h, pad_w: -pad_w, :]
If you use 'valid' padding then pad_w and pad_h would be 0 which will put an empty array in dA.
dA[i, :, :, :] = da_pad[0: -0, 0: -0, :]
I've looked at the code and in layers/convolution.py line 156:
If you use 'valid' padding then pad_w and pad_h would be 0 which will put an empty array in dA.