Python: Bug fix for Redis TypeError

[moonbox3]

Motivation and Context

When using RedisChatMessageStore for message storage and calling thread.serialize(), the following error occurs:

File "/Users/worker/workspace/project/agent-framework-demo/chatagent_redisstore_demo.py", line 93, in chat_demo
    serialized_thread = await thread_1.serialize()
File ".../agent_framework/_threads.py", line 430, in serialize
    state = AgentThreadState(
        service_thread_id=self._service_thread_id, chat_message_store_state=chat_message_store_state
    )
File ".../agent_framework/_threads.py", line 175, in __init__
    self.chat_message_store_state = ChatMessageStoreState.from_dict(chat_message_store_state)
File ".../agent_framework/_serialization.py", line 552, in from_dict
    return cls(**kwargs)
File ".../agent_framework/_threads.py", line 144, in __init__
    raise TypeError("Messages should be a list")

The bug is in ChatMessageStoreState.__init__() in _threads where in the constructor, the line if not isinstance(messages, list): always runs, even if messages is None. When RedisChatMessageStore.serialize() returns a dict without a messages field (containing only thread_id, redis_url, etc.), the messages parameter defaults to None, triggering the TypeError.

The fix is to add an early return after handling the empty/None case - no further processing is necessary because the incoming messages are None.

Description

• Closes Python: When using RedisChatMessageStore for message storage, the following error occurs: TypeError: Messages should be a list. #1991
• Adds tests for coverage.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_threads.py	136	21	84%	145, 177–178, 180, 257–260, 343, 355, 467–471, 474–475, 494, 496, 499, 505
TOTAL	15462	2352	84%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2225	130 💤	0 ❌	0 🔥	56.934s ⏱️

[Copilot]

Pull request overview

This PR fixes a bug in ChatMessageStoreState.__init__() where a TypeError was raised when messages parameter was None or empty. This occurred when using RedisChatMessageStore with AgentThread.serialize() because Redis stores don't include a messages field in their serialized state.

• Fixed the TypeError by adding an early return after handling None/empty messages
• Added comprehensive test coverage for the None and empty messages scenarios
• Added integration test to verify the fix works with RedisChatMessageStore and AgentThread

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
python/packages/core/agent_framework/_threads.py	Added early return in ChatMessageStoreState.__init__() after handling None/empty messages to prevent TypeError
python/packages/core/tests/core/test_threads.py	Added unit tests for None messages, no messages argument, and AgentThreadState with store state without messages field
python/packages/redis/tests/test_redis_chat_message_store.py	Added integration test to verify RedisChatMessageStore can be serialized within an AgentThread