Error occurs when training multiple classes

[bw9623]

Hello, I understand that the angle of the project is basically set from 0 to 90, and we have modified it to 0 to 360 and have used it well when the class num is 1 However, if the class num is more than 2, the following error occurs Do you know anything?
Thank you.

Traceback (most recent call last):
File "./yolov5/train.py", line 600, in
main(opt)
File "./yolov5/train.py", line 498, in main
train(opt.hyp, opt, device)
File "./yolov5/train.py", line 363, in train
compute_loss=compute_loss)
File "/home/training1/anaconda3/envs/cube/lib/python3.7/site-packages/torch/autograd/grad_mode.py", line 26, in decorate_context
return func(*args, **kwargs)
File "/home/training1/cube_detector/yolov5/val.py", line 211, in run
out = non_max_suppression(out, conf_thres, iou_thres, labels=lb, multi_label=True, agnostic=single_cls)
File "/home/training1/cube_detector/yolov5/utils/general.py", line 565, in non_max_suppression
conf_angle, j_angle = x[i, 5+nc:].max(1, keepdim=True)
RuntimeError: cannot perform reduction function max on tensor with no elements because the operation does not have an identity