Trainer.fit() crashes if no checkpoint callback is provided
I hope it's okay that I keep posting issues...
Now that I can circumvent the github installation issues, I pulled in the latests master and let my simple CoolModel demo code run. But now calling trainer.fit() crashes with:

AttributeError                            Traceback (most recent call last)
 in 
21                  )
22
---> 23 trainer.fit(model)
24 # exp.close()


/opt/miniconda3/envs/dev_pytorch_lightning36/lib/python3.6/site-packages/pytorch_lightning/models/trainer.py in fit(self, model)
494                 self.optimizers, self.lr_schedulers = self.optimizers
495
--> 496             self.__run_pretrain_routine(model)
497
498         # return 1 when finished


/opt/miniconda3/envs/dev_pytorch_lightning36/lib/python3.6/site-packages/pytorch_lightning/models/trainer.py in __run_pretrain_routine(self, model)
680
681         # restore training and model before hpc call
--> 682         self.restore_state_if_existing_checkpoint()
683
684         # enable cluster checkpointing


/opt/miniconda3/envs/dev_pytorch_lightning36/lib/python3.6/site-packages/pytorch_lightning/models/trainer.py in restore_state_if_existing_checkpoint(self)
261
262         # find last epoch
--> 263         checkpoints = os.listdir(self.checkpoint_callback.filepath)
264         for name in checkpoints:
265             # ignore hpc ckpts


AttributeError: 'NoneType' object has no attribute 'filepath'

Looking at the code, it appears to happen because I did not provide a checkpoint callback and it tries to access it in restore_state_if_existing_checkpoint