langchain-ai/langgraph · error · InvalidUpdateError

Cannot send a packet to the END node

Error message

Cannot send a packet to the END node

What it means

Error "Cannot send a packet to the END node" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/graph/_branch.py:210

    def _finish(
        self,
        writer: _Writer,
        input: Any,
        result: Any,
        config: RunnableConfig,
    ) -> Runnable | Any:
        if not isinstance(result, (list, tuple)):
            result = [result]
        if self.ends:
            destinations: Sequence[Send | str] = [
                r if isinstance(r, Send) else self.ends[r] for r in result
            ]
        else:
            destinations = cast(Sequence[Send | str], result)
        if any(dest is None or dest == START for dest in destinations):
            raise ValueError("Branch did not return a valid destination")
        if any(p.node == END for p in destinations if isinstance(p, Send)):
            raise InvalidUpdateError("Cannot send a packet to the END node")
        entries = writer(destinations, False)
        if not entries:
            return input
        else:
            need_passthrough = False
            for e in entries:
                if isinstance(e, ChannelWriteEntry):
                    if e.value is PASSTHROUGH:
                        need_passthrough = True
                        break
            if need_passthrough:
                return ChannelWrite(entries)
            else:
                ChannelWrite.do_write(config, entries)
                return input

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/graph/_branch.py:210 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/9f6f870adcccad7e. Report an issue: GitHub.