半监督训练的时候报错，错误如下

Epoch gpu_mem labels img_size box obj cls loss ss_box ss_obj ss_cls tp fp_cls fp_loc pse_num gt_num
27/45 10.1G 33 640 0.03321 0.01326 0.00238 0.3907 0.0272 0.004985 0.001648 0.8537 0 0.4029 1.072 0.9201: 100%|#| 66Traceback (most recent call last):
File "train.py", line 84, in
main(opt)
File "train.py", line 76, in main
trainer.train(callbacks, val)
File "/root/autodl-tmp/semi/5-efficientteacher/trainer/trainer.py", line 536, in train
self.after_epoch(callbacks, val)
File "/root/autodl-tmp/semi/5-efficientteacher/trainer/ssod_trainer.py", line 329, in after_epoch
self.semi_ema.update_decay(self.epoch - self.cfg.hyp.burn_epochs)
AttributeError: 'NoneType' object has no attribute 'update_decay'