Exporting the operator ::flatten_dense_tensors to ONNX opset version 12 is not supported

deployment
1

I am trying to export my model to ONNX, but get the Error,

Traceback (most recent call last):
  File "/home/code/2022/SR/BigViT1x/basicsr/train.py", line 223, in <module>
    train_pipeline(root_path)
  File "/home/code/2022/SR/BigViT1x/basicsr/train.py", line 195, in train_pipeline
    model.save_to_onnx()
  File "/home/code/2022/SR/BigViT1x/basicsr/models/sr_model.py", line 248, in save_to_onnx
    torch.onnx.export(self.net_g,  # model being run
  File "/home/anaconda3.9/lib/python3.9/site-packages/torch/onnx/__init__.py", line 350, in export
    return utils.export(
  File "/home/anaconda3.9/lib/python3.9/site-packages/torch/onnx/utils.py", line 163, in export
    _export(
  File "/home/anaconda3.9/lib/python3.9/site-packages/torch/onnx/utils.py", line 1074, in _export
    graph, params_dict, torch_out = _model_to_graph(
  File "/home/anaconda3.9/lib/python3.9/site-packages/torch/onnx/utils.py", line 731, in _model_to_graph
    graph = _optimize_graph(
  File "/home/anaconda3.9/lib/python3.9/site-packages/torch/onnx/utils.py", line 308, in _optimize_graph
    graph = _C._jit_pass_onnx(graph, operator_export_type)
  File "/home/anaconda3.9/lib/python3.9/site-packages/torch/onnx/__init__.py", line 416, in _run_symbolic_function
    return utils._run_symbolic_function(*args, **kwargs)
  File "/home/anaconda3.9/lib/python3.9/site-packages/torch/onnx/utils.py", line 1421, in _run_symbolic_function
    raise symbolic_registry.UnsupportedOperatorError(
torch.onnx.symbolic_registry.UnsupportedOperatorError: Exporting the operator ::flatten_dense_tensors to ONNX opset version 12 is not supported. Please feel free to request support or submit a pull request on PyTorch GitHub.

I have no idea how to solve the issue.

Thank you.