From 488db577e2e2ba9b4d2c23df3b079f007356af05 Mon Sep 17 00:00:00 2001
From: Jackjin <1037461232@qq.com>
Date: Sun, 1 Feb 2026 05:17:39 +0800
Subject: [PATCH] fix(core): prevent crash in ParrotFakeChatModel when messages
 list is empty (#34943)

---
 libs/core/langchain_core/language_models/fake_chat_models.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libs/core/langchain_core/language_models/fake_chat_models.py b/libs/core/langchain_core/language_models/fake_chat_models.py
index 7ffb5896013..12e5a73fdf5 100644
--- a/libs/core/langchain_core/language_models/fake_chat_models.py
+++ b/libs/core/langchain_core/language_models/fake_chat_models.py
@@ -386,6 +386,9 @@ class ParrotFakeChatModel(BaseChatModel):
         run_manager: CallbackManagerForLLMRun | None = None,
         **kwargs: Any,
     ) -> ChatResult:
+        if not messages:
+            msg = "messages list cannot be empty."
+            raise ValueError(msg)
         return ChatResult(generations=[ChatGeneration(message=messages[-1])])
 
     @property