Missing attribute "training_step_output_for_epoch_end"
I used the documentation way of stopping the training (https://pytorch-lightning.readthedocs.io/en/latest/early_stopping.html#enable-early-stopping-using-callbacks-on-epoch-end).
If on_bath_start method returns -1 at the very beginning of an epoch, the titled AttributeError exception.
The problem is in training_loop.py line 496 (batch_output.training_step_output_for_epoch_end).
Code sample
Use the method and run your code:
    def on_batch_start(self, batch):
        return -1
Expected behavior
Check batch_output value if equals -1 before running trainin_loop.py line 495.
The early stopping method achieved the same way the documentation specifies should not throw an exception but rather simply stop the training.

Environment

CUDA:

GPU:
available:         False
version:           None


Packages:

numpy:             1.19.1
pyTorch_debug:     False
pyTorch_version:   1.6.0
pytorch-lightning: 0.9.0
tqdm:              4.49.0


System:

OS:                Windows
architecture:

64bit
WindowsPE


processor:         Intel64 Family 6 Model 60 Stepping 3, GenuineIntel
python:            3.8.5
version:           10.0.18362