Bug:AttributeError: 'AgentPPO' object has no attribute 'reward_tracker'

Traceback (most recent call last):
File "/Applications/PyCharm.app/Contents/plugins/python/helpers/pydev/pydevd.py", line 1491, in _exec
pydev_imports.execfile(file, globals, locals) # execute the script
File "/Applications/PyCharm.app/Contents/plugins/python/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
exec(compile(contents+"\n", file, 'exec'), glob, loc)
File "/Users/……/FinRL/finrl/main.py", line 149, in
raise SystemExit(main())
File "/Users/……/FinRL/finrl/main.py", line 68, in main
train(
File "/Users/……/FinRL/finrl/train.py", line 60, in train
trained_model = agent.train_model(
File "/Users/……/FinRL/finrl/agents/elegantrl/models.py", line 84, in train_model
train_and_evaluate(model)
File "/Users/……ElegantRL/elegantrl/train/run.py", line 120, in train_and_evaluate
r_exp = agent.reward_tracker.mean()
AttributeError: 'AgentPPO' object has no attribute 'reward_tracker'