It seems that the implementation of the PhotoWCT model doesn’t use the standard forward methods as seen in these lines of code 68, but instead apparently relies on the transform function.
The ONNX export however, uses the forward method to call the model, which would return None at the moment. I don’t know, why the model authors skipped these standard implementation and instead went with the custom transform method (which would also break any data parallel approach etc.).
Anyway, you could monkey patch the model by assigning the transform to p_wct.forward and make sure the model executes properly in eager mode before trying to export it.
After I’ve patched the method, it seems that more errors are raised.