langchain-ai/langgraph · error · ValueError

Node name must be provided if action is not a function

Error message

Node name must be provided if action is not a function

What it means

Error "Node name must be provided if action is not a function" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/graph/state.py:785

                retry_policy = retry  # type: ignore[assignment]

        if (input_ := kwargs.get("input", MISSING)) is not MISSING:
            warnings.warn(
                "`input` is deprecated and will be removed. Please use `input_schema` instead.",
                category=LangGraphDeprecatedSinceV05,
            )
            if input_schema is None:
                input_schema = cast(type[NodeInputT] | None, input_)
        timeout = coerce_timeout_policy(timeout)

        if not isinstance(node, str):
            action = node
            if isinstance(action, Runnable):
                node = action.get_name()
            else:
                node = getattr(action, "__name__", action.__class__.__name__)
            if node is None:
                raise ValueError(
                    "Node name must be provided if action is not a function"
                )
        if self.compiled:
            logger.warning(
                "Adding a node to a graph that has already been compiled. This will "
                "not be reflected in the compiled graph."
            )
        if not isinstance(node, str):
            action = node
            node = cast(str, getattr(action, "name", getattr(action, "__name__", None)))
            if node is None:
                raise ValueError(
                    "Node name must be provided if action is not a function"
                )
        if action is None:
            raise RuntimeError
        if node in self.nodes:
            raise ValueError(f"Node `{node}` already present.")

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/graph/state.py:785 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/9a27ca4ef9a66c06. Report an issue: GitHub.