请问大神，pb模型转rknn报错，'NoneType' object has no attribute 'ge...

请问大神，pb模型转rknn报错，'NoneType' object has no attribute 'get_input_layers'是怎么回事

--> Loading model
done
--> Building model
E Model file [./pb_cnn_model/pb_two/saved_model.pb] does not exist!
Traceback (most recent call last):
  File "/home/lyb2/文档/12.13/rknn_transfer.py", line 24, in <module>
    rknn.build(do_quantization=False, dataset='./dataset.txt', pre_compile=True)
  File "/home/lyb2/.pyenv/versions/3.6.9/lib/python3.6/site-packages/rknn/api/rknn.py", line 220, in build
    inputs = self.rknn_base.net.get_input_layers()
AttributeError: 'NoneType' object has no attribute 'get_input_layers'

Process finished with exit code 1