Merge pull request #22 from mikcnt/bug/no-metadata-checkpoint

Remove metadata key from checkpoint when not used

Author: lucmos

src/nn_core/callbacks.py

@@ -53,4 +53,6 @@ def on_save_checkpoint(
     ) -> None:
         if self._is_nnlogger(trainer):
             trainer.logger.on_save_checkpoint(trainer=trainer, pl_module=pl_module, checkpoint=checkpoint)
-            checkpoint[METADATA_KEY] = trainer.datamodule.metadata
+            metadata = getattr(trainer.datamodule, "metadata", None)
+            if metadata is not None:
+                checkpoint[METADATA_KEY] = metadata