Initialise to None

libs/langgraph/langgraph/pregel/loop.py

@@ -250,13 +250,7 @@ class PregelLoop:
             if self.config[CONF].get(CONFIG_KEY_CHECKPOINT_NS)
             else ()
         )
-        self.prev_checkpoint_config = (
-            self.checkpoint_config
-            if self.checkpoint_config
-            and CONF in self.checkpoint_config
-            and CONFIG_KEY_CHECKPOINT_ID in self.checkpoint_config[CONF]
-            else None
-        )
+        self.prev_checkpoint_config = None
 
     def put_writes(self, task_id: str, writes: Sequence[tuple[str, Any]]) -> None:
         """Put writes for a task, to be read by the next tick."""