From aa4f70d762bf78408d26288b9b69e66bb811f0ed Mon Sep 17 00:00:00 2001
From: Kris <adwerrd@hotmail.com>
Date: Thu, 9 Apr 2026 14:02:49 +0800
Subject: [PATCH] fix(ui): add missing optional chaining for activeResponse in
 makeRequest finally block
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When two `makeRequest` calls run concurrently (e.g. `sendMessage` + `resumeStream`),
the first to complete sets `this.activeResponse = undefined` in its finally block.
The second call's finally block then crashes with:
`TypeError: Cannot read properties of undefined (reading 'state')`

This happened because `this.activeResponse!.state.message` used a non-null assertion
instead of optional chaining, while `this.activeResponse?.state.finishReason` on the
very next property already used `?.` — an inconsistency.

Changes:
- Replace `this.activeResponse!.state.message` with `this.activeResponse?.state?.message`
- Add `?.` to `this.activeResponse?.state?.finishReason` for consistency
- Update `ChatOnFinishCallback` type to reflect that `message` can be `undefined`
---
 packages/ai/src/ui/chat.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ai/src/ui/chat.ts b/packages/ai/src/ui/chat.ts
index 6dbd3c661c8f..990d2d8ab27b 100644
--- a/packages/ai/src/ui/chat.ts
+++ b/packages/ai/src/ui/chat.ts
@@ -172,7 +172,7 @@ export type ChatOnDataCallback<UI_MESSAGE extends UIMessage> = (
  * @param finishReason The reason why the generation finished.
  */
 export type ChatOnFinishCallback<UI_MESSAGE extends UIMessage> = (options: {
-  message: UI_MESSAGE;
+  message: UI_MESSAGE | undefined;
   messages: UI_MESSAGE[];
   isAbort: boolean;
   isDisconnect: boolean;
@@ -758,12 +758,12 @@ export abstract class AbstractChat<UI_MESSAGE extends UIMessage> {
     } finally {
       try {
         this.onFinish?.({
-          message: this.activeResponse!.state.message,
+          message: this.activeResponse?.state?.message,
           messages: this.state.messages,
           isAbort,
           isDisconnect,
           isError,
-          finishReason: this.activeResponse?.state.finishReason,
+          finishReason: this.activeResponse?.state?.finishReason,
         });
       } catch (err) {
         console.error(err);