[checkpoint logic] Fix bug which doesn't account for NoneType for `mo…

…del.hparams` (#1817)

The intention of the code is to output a warning message when `hparams`
is null or not set. Instead the code now fatals when
`model.hparams = None`. Prevent that.

pytorch_lightning/trainer/training_io.py

@@ -342,7 +342,7 @@ def dump_checkpoint(self):
         if self.use_amp and self.use_native_amp:
             checkpoint['native_amp_scaling_state'] = self.scaler.state_dict()
 
-        if hasattr(model, "hparams"):
+        if hasattr(model, "hparams") and model.hparams is not None:
             parsing.clean_namespace(model.hparams)
             checkpoint['hparams_type'] = model.hparams.__class__.__name__
             if checkpoint['hparams_type'] == 'dict':