INVALID_GRAPH_NODE_RETURN_VALUE

import { z } from "zod/v4";
import { StateGraph, StateSchema, GraphNode } from "@langchain/langgraph";

const State = new StateSchema({
  someKey: z.string(),
});

const badNode: GraphNode<typeof State> = (state) => {
  // Should return an object with a value for "someKey", not an array
  return ["whoops"];
};

const builder = new StateGraph(State).addNode("badNode", badNode);
// ...

const graph = builder.compile();

await graph.invoke({ someKey: "someval" });

InvalidUpdateError: Expected object, got ['whoops']
For troubleshooting, visit: https://langchain-ai.github.io/langgraphjs/troubleshooting/errors/INVALID_GRAPH_NODE_RETURN_VALUE