[BUG] AttributeError in AgentCoreMemorySessionManager when created_message is None

[Sami-Tanquary]

Describe the bug
When using Strands agents with tool calls on the AgentCore runtime, applying the upstream OpenTelemetry fix for Bedrock ConverseStream responses (PR #3990) consistently exposes a failure in the AgentCore Memory Strands session manager during message persistence.

Specifically, AgentCoreMemorySessionManager.append_message assumes the memory “create message/event” call always returns a dict, and crashes when it returns None:

created_message.get("eventId")
# AttributeError: 'NoneType' object has no attribute 'get'

This occurs when the session manager hook attempts to persist Strands message events generated during tool-use flows.

To Reproduce
Steps to reproduce the behavior:

1. Deploy a Strands agent configured to use AgentCore Memory on the AgentCore runtime.

2. Enable tool calling on the agent.

3. Apply the upstream OpenTelemetry Bedrock ConverseStream guard (PR #3990) to avoid the KeyError: 'output' crash (the runtime currently injects an AWS OpenTelemetry distro that predates this fix).

4. Invoke a tool during a normal agent turn (toolUse → toolResult).

5. Observe the agent invocation fail with:

AttributeError: 'NoneType' object has no attribute 'get'
  at bedrock_agentcore/memory/integrations/strands/session_manager.py:488

Expected behavior

• Applying the upstream OpenTelemetry fix should allow execution to proceed normally.

• If a memory persistence call fails or returns an empty response, the AgentCore Memory session manager should handle it gracefully (or surface a clear error), rather than crashing the agent event loop.

• Tool-use flows should not cause unhandled exceptions during memory message persistence.

Screenshots
N/A (stack trace and logs available).

Desktop (please complete the following information):
OS: Linux (AgentCore managed runtime)
Runtime: AWS Bedrock AgentCore
Python: 3.13
Strands Agents: 1.21.0
bedrock-agentcore: 1.2.0

Additional context

• The AgentCore runtime injects an AWS OpenTelemetry distro (telemetry.auto.version: 0.12.2-aws) that does not yet include the upstream OpenTelemetry fix for Bedrock ConverseStream (PR #3990).

• Applying that fix via monkey patch unblocks execution but consistently exposes this separate failure in the AgentCore Memory Strands integration.

• The failure occurs when the session manager hook attempts to persist Strands message events produced during tool-use flows; the persistence call returns None, which is not currently guarded against.

[mustafashabib]

@Sami-Tanquary and team --

Confirming this is still present in bedrock-agentcore==1.3.0. Hit this in production today.

Environment:

• bedrock-agentcore==1.3.0
• strands-agents==1.24.0
• aws-opentelemetry-distro==0.15.0
• Python 3.14, AgentCore managed runtime

Production stack trace:

Traceback (most recent call last):
  File "/usr/local/lib/python3.14/site-packages/strands/event_loop/event_loop.py", line 409, in
_handle_model_execution
    await agent.hooks.invoke_callbacks_async(MessageAddedEvent(agent=agent, message=message))
  File "/usr/local/lib/python3.14/site-packages/strands/hooks/registry.py", line 236, in
invoke_callbacks_async
    callback(event)
  File "/usr/local/lib/python3.14/site-packages/strands/session/session_manager.py", line 46, in
<lambda>
    registry.add_callback(MessageAddedEvent, lambda event: self.append_message(event.message,
event.agent))
  File "/usr/local/lib/python3.14/site-packages/bedrock_agentcore/memory/integrations/strands/session_ma
nager.py", line 571, in append_message
    session_message = SessionMessage.from_message(message, created_message.get("eventId"))
AttributeError: 'NoneType' object has no attribute 'get'

append_message (line 570) calls create_message, which returns None when
AgentCoreMemoryConverter.message_to_payload() produces an empty list (line 421-422). The missing guard is at line 571 — it calls .get("eventId") on None without checking.

Workaround: We monkey-patch append_message after constructing the session manager:

from strands.types.session import SessionMessage

def _safe_append_message(message, agent, **kwargs):
    created_message = session_mgr.create_message(
        session_mgr.session_id,
        agent.agent_id,
        SessionMessage.from_message(message, 0),
    )
    if created_message is None:
        return
    session_message = SessionMessage.from_message(message, created_message.get("eventId"))
    session_mgr._latest_agent_message[agent.agent_id] = session_message

session_mgr.append_message = _safe_append_message

But I think the real fix is to modify append_message at line 571:

def append_message(self, message, agent, **kwargs):
    created_message = self.create_message(self.session_id, agent.agent_id,
SessionMessage.from_message(message, 0))
    if created_message is None:
        return
    session_message = SessionMessage.from_message(message, created_message.get("eventId"))
    self._latest_agent_message[agent.agent_id] = session_message

[linzhlalala]

Confirming this is still present in bedrock-agentcore==1.4.0.

With the monkey-patch, I get:

Agent Response: {'status': 'error', 'error': 'An error occurred (ValidationException) when calling the ConverseStream operation: The text field in the ContentBlock object at messages.2.content.0 is blank. Add text to the text field, and try again.'}

[Kevanov88]

bedrock-agentcore[strands-agents]==1.4.0

We’re using streaming with strand agents and tried the monkey-patch. It hides the error, but we no longer receive the contentBlockDelta chunks.

While I could generate a fake eventId, I’m concerned that this might introduce issues elsewhere, particularly with short-term memory handling.