训练时,报下面的错误,请问怎么解决?

Traceback (most recent call last):
File "train.py", line 174, in
main()
File "train.py", line 170, in main
train.start_train()
File "train.py", line 148, in start_train
X_train, X_test, y_train, y_test=self.load_data()
File "train.py", line 55, in load_data
_, w, h = img.shape[::-1]
AttributeError: 'NoneType' object has no attribute 'shape'