Calling module.log(...) within a callback fails
🐛 Bug
Calling pl_module.log(...) within a Callback fails, even though this is recommended by the documentation here: https://pytorch-lightning.readthedocs.io/en/latest/loggers.html#logging-from-a-callback
Error
  File "my_callback_file.py", line XX, in on_validation_epoch_end
    pl_module.log_dict(my_metrics_dict)
  File "/home/local/USHERBROOKE/pain5474/opt/miniconda3/envs/cav/lib/python3.8/site-packages/pytorch_lightning/core/lightning.py", line 287, in log_dict
    self.log(
  File "/home/local/USHERBROOKE/pain5474/opt/miniconda3/envs/cav/lib/python3.8/site-packages/pytorch_lightning/core/lightning.py", line 233, in log
    self._results.log(
  File "/home/local/USHERBROOKE/pain5474/opt/miniconda3/envs/cav/lib/python3.8/site-packages/pytorch_lightning/core/step_result.py", line 171, in log
    self.__set_meta(
  File "/home/local/USHERBROOKE/pain5474/opt/miniconda3/envs/cav/lib/python3.8/site-packages/pytorch_lightning/core/step_result.py", line 217, in __set_meta
    _internal = self['meta']['_internal']
KeyError: '_internal'
python-BaseException

cc @nathanpainchaud
This is happening on master
Expected behavior

We can log from callbacks using the lightning module
Environment
Happening on PyTorch Lightning master