AttributeError: 'NoneType' object has no attribute 'cpu'

[Peac12]

hi , please can you help me
I was doing every step , but i face this problem in detector.py :
YOLOX_deepsort_tracker/detector.py", line 51, in detect
outputs = postprocess(
AttributeError: 'NoneType' object has no attribute 'cpu'

the code in detecto.py is :
with torch.no_grad():
outputs = self.model(img)
outputs = postprocess(
outputs, self.exp.num_classes, self.exp.test_conf, self.exp.nmsthre # TODO:用户可更改
)[0].cpu().numpy()