Loading a model from PL 1.2 that was saved in PL 1.1 breaks
🐛 Bug
I saved a model trained with PL 1.1 from an environment with PL 1.2 and it breaks. There are some PL specific objects that get pickled into the checkpoint. This shouldn't happen. See error below:
Traceback (most recent call last):
  File "scripts/train_bart_seq2seq_augmented_kilt.py", line 45, in <module>
    model = BartSeq2SeqAugmented(**vars(args))
  File "/home/ndecao/modify-transformers-memory/src/models/bart_seq2seq_augmented_kilt.py", line 67, in __init__
    self.model = BartSeq2Seq.load_from_checkpoint(self.hparams.model_checkpoint)
  File "/home/ndecao/.anaconda3/envs/kilt37/lib/python3.7/site-packages/pytorch_lightning/core/saving.py", line 134, in load_from_checkpoint
    checkpoint = pl_load(checkpoint_path, map_location=lambda storage, loc: storage)
  File "/home/ndecao/.anaconda3/envs/kilt37/lib/python3.7/site-packages/pytorch_lightning/utilities/cloud_io.py", line 32, in load
    return torch.load(f, map_location=map_location)
  File "/home/ndecao/.anaconda3/envs/kilt37/lib/python3.7/site-packages/torch/serialization.py", line 594, in load
    return _load(opened_zipfile, map_location, pickle_module, **pickle_load_args)
  File "/home/ndecao/.anaconda3/envs/kilt37/lib/python3.7/site-packages/torch/serialization.py", line 853, in _load
    result = unpickler.load()
AttributeError: Can't get attribute '_gpus_arg_default' on <module 'pytorch_lightning.utilities.argparse_utils'

Expected behavior
The model should load without any error.
Environment
The model was trained and saved using PL 1.1.6 and loaded from PL 1.2.1

PyTorch Version (e.g., 1.0): 1.7.1
OS (e.g., Linux): Linux
Python version: 3.9