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### Description https://github.com/langchain-ai/langgraph/issues/6137 and https://github.com/langchain-ai/langgraph/issues/5677 reported issues where older checkpoints read by AsyncPostgresSaver/PostgresSaver from `langgraph-checkpoint-postgres==2.0.19` fail to read channel values, throwing `NoneType object is not a mapping`. This was due to a bug in how `channel_values` is assembled: ```python "channel_values": { **value["checkpoint"].get("channel_values"), # <--- if channel_values doesn't exist (old checkpoint), **None errors **self._load_blobs(value["channel_values"]), }, ``` This bug was observed for checkpoints generated by `langgraph-checkpoint-postgres<=2.0.19`. Fixed by providing a fallback to `value["checkpoint"].get("channel_values")`: ```python **value["checkpoint"], "channel_values": { **( value["checkpoint"].get("channel_values") or {} ), # 'or {}' needed for backwards compat with v3 checkpoints and below, as v4 introduced channel_values key **self._load_blobs(value["channel_values"]), }, ``` ### Tests Added test for AsyncPostgresSaver and test for PostgresSaver, using monkeypatch to remove `channel_values` before CheckpointTuple is assembled in `_load_checkpoint_tuple`. ### Solves https://github.com/langchain-ai/langgraph/issues/6137 and https://github.com/langchain-ai/langgraph/issues/5677 --------- Co-authored-by: Shahrukh Shaik <144558473+shahrukh-shaik@users.noreply.github.com>