RuntimeError: cannot perform reduction function

Training START
into model/fit
Traceback (most recent call last):
File "train.py", line 21, in
m.fit()
File "/home/caodongjiang/gait/gaitSet-master/model/model.py", line 174, in fit
) = self.triplet_loss(triplet_feature, triplet_label)
File "/home/caodongjiang/anaconda3/envs/gaitSet/lib/python3.6/site-packages/torch/nn/modules/module.py", line 493, in __call__
result = self.forward(*input, **kwargs)
File "/home/caodongjiang/anaconda3/envs/gaitSet/lib/python3.6/site-packages/torch/nn/parallel/data_parallel.py", line 152, in forward
outputs = self.parallel_apply(replicas, inputs, kwargs)
File "/home/caodongjiang/anaconda3/envs/gaitSet/lib/python3.6/site-packages/torch/nn/parallel/data_parallel.py", line 162, in parallel_apply
return parallel_apply(replicas, inputs, kwargs, self.device_ids[:len(replicas)])
File "/home/caodongjiang/anaconda3/envs/gaitSet/lib/python3.6/site-packages/torch/nn/parallel/parallel_apply.py", line 83, in parallel_apply
raise output
File "/home/caodongjiang/anaconda3/envs/gaitSet/lib/python3.6/site-packages/torch/nn/parallel/parallel_apply.py", line 59, in _worker
output = module(*input, **kwargs)
File "/home/caodongjiang/anaconda3/envs/gaitSet/lib/python3.6/site-packages/torch/nn/modules/module.py", line 493, in __call__
result = self.forward(*input, **kwargs)
File "/home/caodongjiang/gait/gaitSet-master/model/network/triplet.py", line 23, in forward
hard_hn_dist = torch.min(torch.masked_select(dist, hn_mask).view(n, m, -1), 2)[0]
**RuntimeError: cannot perform reduction function min on tensor with no elements because the operation does not have an identity**