NameError: free variable 'device' referenced before assignment in enclosing scope

[ssstitch]

No description provided.

[ssstitch]

I run the main.py with
--data_test
Set5
--scale
4
--pre_train
/home/stitch/EDSR-PyTorch-master/experiment/test/model/EDSR_x4.pt
--test_only
--save_results

occered this error
Evaluation:
0%| | 0/5 [00:00<?, ?it/s]
Traceback (most recent call last):
File "/home/stitch/EDSR-PyTorch-master/src/main.py", line 33, in
main()
File "/home/stitch/EDSR-PyTorch-master/src/main.py", line 26, in main
while not t.terminate():
File "/home/stitch/EDSR-PyTorch-master/src/trainer.py", line 147, in terminate
self.test()
File "/home/stitch/EDSR-PyTorch-master/src/trainer.py", line 90, in test
lr, hr = self.prepare(lr, hr)
File "/home/stitch/EDSR-PyTorch-master/src/trainer.py", line 143, in prepare
return [_prepare(a) for a in args]
File "/home/stitch/EDSR-PyTorch-master/src/trainer.py", line 143, in
return [_prepare(a) for a in args]
File "/home/stitch/EDSR-PyTorch-master/src/trainer.py", line 141, in _prepare
return tensor.to(device)
NameError: free variable 'device' referenced before assignment in enclosing scope

what should I do,thanks