Error when Implementing training_epoch_end() for GAN example
🐛 Bug
To Reproduce
Steps to reproduce the behavior:

Go to GAN example
Install latest version of pytorch-lightning (0.9.0)

pip install pytorch-lightning==0.9.0

Implement training_epoch_end() method for GAN class

def training_epoch_end(self, outputs):
    return outputs

Run training code cell

gan_model = GAN(hparams)

trainer = pl.Trainer(gpus=1)    
trainer.fit(gan_model)   

See error

    138         # all keys not progress_bar or log are candidates for callbacks
    139         callback_metrics = {}
--> 140         for k, v in output.items():
    141             if k not in ['progress_bar', 'log', 'hiddens']:
    142                 callback_metrics[k] = v

AttributeError: 'list' object has no attribute 'items'

Expected behavior
No Error