runtime error

Traceback (most recent call last): File "/home/user/app/app.py", line 4, in <module> learn = load_learner('model20.pkl') File "/home/user/.local/lib/python3.10/site-packages/fastai/learner.py", line 446, in load_learner try: res = torch.load(fname, map_location=map_loc, pickle_module=pickle_module) File "/home/user/.local/lib/python3.10/site-packages/torch/serialization.py", line 809, in load return _load(opened_zipfile, map_location, pickle_module, **pickle_load_args) File "/home/user/.local/lib/python3.10/site-packages/torch/serialization.py", line 1172, in _load result = unpickler.load() File "/home/user/.local/lib/python3.10/site-packages/torch/serialization.py", line 1165, in find_class return super().find_class(mod_name, name) AttributeError: Custom classes or functions exported with your `Learner` not available in namespace.\Re-declare/import before loading: Can't get attribute 'FlattenedLoss' on <module 'fastai.layers' from '/home/user/.local/lib/python3.10/site-packages/fastai/layers.py'>

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