When I used the Window system to train the code, the code reported an error：'>' not supported between instances of 'NoneType' and 'int'

Traceback (most recent call last):
File "D:/SiamMask/tools/train_siammask.py", line 296, in
main()
File "D:/SiamMask/tools/train_siammask.py", line 170, in main
train(train_loader, dist_model, optimizer, lr_scheduler, args.start_epoch, cfg)
File "D:/SiamMask/tools/train_siammask.py", line 188, in train
for iter, input in enumerate(train_loader):
File "D:\Anaconda\envs\mask\lib\site-packages\torch\utils\data\dataloader.py", line 314, in __next__
batch = self.collate_fn([self.dataset[i] for i in indices])
File "D:\Anaconda\envs\mask\lib\site-packages\torch\utils\data\dataloader.py", line 314, in
batch = self.collate_fn([self.dataset[i] for i in indices])
File "D:\SiamMask\datasets\siam_mask_dataset.py", line 551, in __getitem__
search_mask = (cv2.imread(search[2], 0) > 0).astype(np.float32)
TypeError: '>' not supported between instances of 'NoneType' and 'int'