Fix saving native AMP scaler state (#1777)

Saving was introduced in #1561.

CHANGELOG.md

@@ -46,6 +46,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Fixed lr key name in case of param groups in LearningRateLogger ([#1719](https://github.com/PyTorchLightning/pytorch-lightning/pull/1719))
 
+- Fixed saving native AMP scaler state (introduced in [#1561](https://github.com/PyTorchLightning/pytorch-lightning/pull/1561))
+
+
 ## [0.7.5] - 2020-04-27
 
 ### Changed

pytorch_lightning/trainer/training_io.py

@@ -338,8 +338,8 @@ class TrainerIOMixin(ABC):
 
         checkpoint['state_dict'] = model.state_dict()
 
-        # restore native amp scaling
-        if self.use_amp and self.use_native_amp and 'native_amp_scaling_state' in checkpoint:
+        # save native amp scaling
+        if self.use_amp and self.use_native_amp:
             checkpoint['native_amp_scaling_state'] = self.scaler.state_dict()
 
         if hasattr(model, "hparams"):