[BugFix] Do not reload empty buffers

benchmarl/experiment/experiment.py

@@ -815,7 +815,7 @@ def state_dict(self) -> OrderedDict:
             state=state,
             **{f"loss_{k}": item.state_dict() for k, item in self.losses.items()},
             **{
-                f"buffer_{k}": item.state_dict()
+                f"buffer_{k}": item.state_dict() if len(item) else None
                 for k, item in self.replay_buffers.items()
             },
         )
@@ -832,7 +832,10 @@ def load_state_dict(self, state_dict: Dict) -> None:
         """
         for group in self.group_map.keys():
             self.losses[group].load_state_dict(state_dict[f"loss_{group}"])
-            self.replay_buffers[group].load_state_dict(state_dict[f"buffer_{group}"])
+            if state_dict[f"buffer_{group}"] is not None:
+                self.replay_buffers[group].load_state_dict(
+                    state_dict[f"buffer_{group}"]
+                )
         if not self.config.collect_with_grad:
             self.collector.load_state_dict(state_dict["collector"])
         self.total_time = state_dict["state"]["total_time"]