OpCodeGenerator is unimplemented for Softplus

[juhan]

When trying to convert a Yolov4 ONNX model with onnx-pytorch I get the following error. Seems to be an unimplemented OpCode for Softplus.

WARNING:root:Cannot get default value for dilations of Conv.
WARNING:root:Cannot get default value for kernel_shape of Conv.
WARNING:root:Cannot get default value for pads of Conv.
WARNING:root:Cannot get default value for strides of Conv.
Traceback (most recent call last):
File "/usr/lib/python3.8/runpy.py", line 194, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/lib/python3.8/runpy.py", line 87, in _run_code
exec(code, run_globals)
File "/someenv/lib/python3.8/site-packages/onnx_pytorch/code_gen.py", line 378, in
main()
File "/someenv/python3.8/site-packages/onnx_pytorch/code_gen.py", line 368, in main
gen(onnx_model=args.onnx_model_path,
File "/someenv/python3.8/site-packages/onnx_pytorch/code_gen.py", line 291, in gen
model_code_generator.run()
File "/someenv/python3.8/site-packages/onnx_pytorch/code_gen.py", line 246, in run
raise NotImplementedError(
NotImplementedError: OpCodeGenerator is unimplemented for Softplus.

Installed version:

pip show onnx_pytorch
Name: onnx-pytorch
Version: 0.1.4
Summary: Convert ONNX to PyTorch code.
Home-page: https://github.com/fumihwh/onnx-pytorch
Author: fumihwh
Author-email: fumihwh@gmail.com
License: Apache 2.0
Location: /someenv/lib/python3.8/site-packages
Requires: torchvision, setuptools, torch, PyYAML, tqdm, onnxruntime, onnx, sympy, pytest, numpy
Required-by:

[fumihwh]

Hi, @juhan could you add support for this op? Contribution is welcome!
Just follow the PRelu, I think it could help.