code: def validation_epoch_end(self, outputs):
      avg_loss = torch.stack([x["val_loss"] for x in outputs]).mean()
      print(avg_loss)
      return {"val_loss": avg_loss}
  
file_path: fastai/nbs/examples/migrating_lightning.py
imports: from fastai.data.load import DataLoader
  import os, torch
  from torch.nn import functional
  from torchvision.datasets import MNIST
  from torchvision import transforms
  from lightning import LightningModule
label_desc: Use image node_id 7 for calling the LitModel obj's underlying member method code with example usage: obj.validation_epoch_end(outputs) and returns: dict