From 2b759a2a33e141f364bfaf570f7b64577744c5d8 Mon Sep 17 00:00:00 2001
From: Tat Dat Duong <david@duong.cz>
Date: Tue, 3 Jun 2025 15:20:13 +0200
Subject: [PATCH] fix(sdk-js): `uiMessageReducer` should handle `undefined`
 metadata

---
 libs/sdk-js/package.json          |  2 +-
 libs/sdk-js/src/react-ui/types.ts | 11 +++++++----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/libs/sdk-js/package.json b/libs/sdk-js/package.json
index 82fad7e1c..6a14597f1 100644
--- a/libs/sdk-js/package.json
+++ b/libs/sdk-js/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@langchain/langgraph-sdk",
-  "version": "0.0.81",
+  "version": "0.0.82",
   "description": "Client library for interacting with the LangGraph API",
   "type": "module",
   "packageManager": "yarn@1.22.19",
diff --git a/libs/sdk-js/src/react-ui/types.ts b/libs/sdk-js/src/react-ui/types.ts
index 32bfe4188..42499996d 100644
--- a/libs/sdk-js/src/react-ui/types.ts
+++ b/libs/sdk-js/src/react-ui/types.ts
@@ -7,7 +7,7 @@ export interface UIMessage<
   id: string;
   name: TName;
   props: TProps;
-  metadata: {
+  metadata?: {
     merge?: boolean;
     run_id?: string;
     name?: string;
@@ -51,9 +51,12 @@ export function uiMessageReducer(
 
     const index = state.findIndex((ui) => ui.id === event.id);
     if (index !== -1) {
-      newState[index] = event.metadata.merge
-        ? { ...event, props: { ...state[index].props, ...event.props } }
-        : event;
+      newState[index] =
+        typeof event.metadata === "object" &&
+        event.metadata != null &&
+        event.metadata.merge
+          ? { ...event, props: { ...state[index].props, ...event.props } }
+          : event;
     } else {
       newState.push(event);
     }