[BUG] The content field in the Message object at messages.XX is empty

[scandura]

Checks

• I have updated to the lastest minor and patch version of Strands
• I have checked the documentation and this is not expected behavior
• I have searched ./issues and there are no duplicates of my issue

Strands Version

1.0.1

Python Version

3.11

Operating System

AWS Lambda

Installation Method

pip

Steps to Reproduce

Create a Agent and a S3 Session Manager and tools to process images with any Anthropic LLM using Bedrock

Expected Behavior

The payload to process messages with ConverseStream have information about to send images, videos and documents for LLMs.

Actual Behavior

When have any message history with media info, the Strands don't format correctly the payload and the application receive the error: An error occurred (ValidationException) when calling the ConverseStream operat

ion: The content field in the Message object at messages.XX is empty. Add a ContentBlock object to the content field and try again.

Additional Context

No response

Possible Solution

There is the method format_request In the class bedrock.py, you can add a check on the messages to avoid empty content block, or detect a image and format correctly the payload.

Related Issues

No response

[murphm8]

I am running into something similar. It seems like there are assistant messages being inserted with no content, for me it appears to be after tool use. This causes the call to Bedrock to fail. I updated remove_blank_messages_content_text to add {"text": "[blank text]"} to the empty content arrays and that fixes the API call failure. I imagine it would be better to not be inserting these messages at all.

{
  "message": {
    "role": "assistant",
    "content": []
  },
  "message_id": 3,
  "redact_message": null,
  "created_at": "2025-07-27T05:21:28.199173+00:00",
  "updated_at": "2025-07-27T05:21:28.199178+00:00"
}

[poshinchen]

I tried to reproduce it using v1.3.0 but I didn't see the exception.

Could you try with the latest v1.3.0 strands-agents, and do you have the code snippet so I can reproduce?

oh I can reproduce it now.

[poshinchen]

I'm seeing different but expected exception. Could you share your code snippet so I can steadily reproduce it?

[poshinchen]

We have a pr ready for mitigation, but since I cannot reproduce it on my end, we need users to provide examples so we could confirm the changes and further go into root causing the issue as follow-up.

[murphm8]

Sorry, I don't have a small reproduction. I was seeing it whenever the agent used a tool, and on the next iteration it would error out because it was calling Bedrock with no content.

[poshinchen]

Is there a chance that you can use this fix and test it?

[poshinchen]

We decided to wait for the reproducible samples so we can fix it in session manager instead of skipping empty content in bedrock.

[poshinchen]

Got the response from customer about how to reproduce: strands-agents/tools#190 (comment), but doesn't look like an issue with session_manager though.

[niyati-22]

I got this error. I am not sure how much of my code I can share for the error, but I'll explain the full process of my code.
My code is following a multi-agent architecture, where other subagents are implemented as tools for the main agent. The agents are quite nested with there being subagents up to 3 levels down from the main agent (main agent-> subagent 1-> subagent2 -> subagent 3, etc). I got this error where after the main-agent's subtask (a subagent implemented as a tool) was done completing, the main agent was calling an mcp tool, and this error appeared.

I hope this provides context!