IndexError: Cannot choose from an empty sequence

[MymengA]

When I act python train.py --dataset sysu

==========
Args:Namespace(arch='resnet50', batch_size=4, dataset='sysu', delta=0.2, gpu='1', img_h=384, img_w=192, log_path='log/', lr=0.1, margin=0.3, method='agw', mode='all', model_path='save_model/', num_pos=4, optim='sgd', resume='', save_epoch=20, seed=0, test_batch=64, test_only=False, trial=1, vis_log_path='log/vis_log/', workers=4)

==> Loading data..
Traceback (most recent call last):
File "train.py", line 133, in
gall_img, gall_label, gall_cam = process_gallery_sysu(data_path, mode=args.mode, trial=1)
File "/home/MMN/data_manager.py", line 58, in process_gallery_sysu
files_rgb.append(random.choice(new_files))
File "/home/anaconda3/envs/lib/python3.7/random.py", line 261, in choice
raise IndexError('Cannot choose from an empty sequence') from None
IndexError: Cannot choose from an empty sequence

Please ask where it might go wrong？