Why is the default implementation for train_dataloader in DataHooks a warning?
The default implementation for these is logging a warning that nothing is implemented. 
  
    
      pytorch-lightning/pytorch_lightning/core/hooks.py
    
    
         Line 529
      in
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           rank_zero_warn("`train_dataloader` must be implemented to be used with the Lightning Trainer") 
        
    
  


Why isn’t the default implementation to raise a NotImplementedError? This would make errors much clearer in case users forget to override these hooks
I believe this is just legacy code. No real reason. It's in the original implementation (to bolts!)
PyTorchLightning/lightning-bolts@797464c
Feel free to try changing it :)