fix broken dcp_saver test (#828)

Summary:
Pull Request resolved: #828

If keys are empty, it seems they are removed during flattening (a step in dcp.save).

Accounting for this change fixes the test
ghstack-source-id: 225758487

Reviewed By: saumishr, diego-urgell

Differential Revision: D57126080

fbshipit-source-id: f713b06f92648e53680d8e9ad071c65fb9f84403

Author: LucasLLC

tests/framework/callbacks/test_dcp_saver.py

@@ -396,7 +396,7 @@ def __init__(self, dataloader: DataLoader) -> None:
 
     def state_dict(self) -> Dict[str, Any]:
         self.state_dict_call_count += 1
-        return {}
+        return {"some_data": 1}
 
     def load_state_dict(self, state_dict: Dict[str, Any]) -> None:
         self.load_state_dict_call_count += 1