Possible error in `update_state` Deciding last updating node because of sorting null values

[xtfocus]

Checked other resources

• [X] I added a very descriptive title to this issue.
• [X] I searched the LangGraph/LangChain documentation with the integrated search.
• [X] I used the GitHub search to find a similar question and didn't find it.
• [X] I am sure that this is a bug in LangGraph/LangChain rather than my code.
• [X] I am sure this is better as an issue rather than a GitHub discussion, since this is a LangGraph bug and not a design question.

Example Code

elif as_node is None:
            last_seen_by_node = sorted(
                (v, n)
                for n, seen in checkpoint["versions_seen"].items()
                for v in seen.values()
            )

Error Message and Stack Trace (if applicable)

No response

Description

This code is taken from https://github.com/langchain-ai/langgraph/blob/51dbbc71b3dfadbc94bd8a8faf8f6fb0b37f63a3/libs/langgraph/langgraph/pregel/__init__.py#L525C1-L530C14 is likely to ignore any node mapped to empty. For instance

{'__start__': {'__start__': '00000000000000000000000000000001.ffee86dada62e095026eb3583d4506fa'},
 'chatbot': {'start:chatbot': '00000000000000000000000000000002.d6f25946c3108fc12f27abbcf9b4cedc'},
 'tools': {}}

System Info

langgraph==0.0.69

[nfcampos]

Do you have an actual error caused by this? I don't think versions seen are ever null?

[nfcampos]

A node mapped to an empty dict is a node which has never run before, so it shouldn't be matched anyway

[xtfocus]

A manual update with as_node not specified can result in empty dict

A node mapped to an empty dict is a node which has never run before, so it shouldn't be matched anyway.