Fix empty assistant message handling in AWS Bedrock Converse API to prevent 400 Bad Request errors

[Sameerlite]

Title

Fix empty assistant message handling in AWS Bedrock Converse API to prevent 400 Bad Request errors

Relevant issues

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Type

🐛 Bug Fix

Changes

Problem

AWS Bedrock Converse API returns a 400 Bad Request error when assistant messages contain empty or whitespace-only text content. The error message is:

"The text field in the ContentBlock object at messages.X.content.0 is blank. Add text to the text field, and try again."

This occurs when users pass messages like:

messages = [
    {"role": "user", "content": "Hello"},
    {"role": "assistant", "content": ""},  # Empty content causes 400 error
    {"role": "user", "content": "How are you?"}
]

Solution

Modified the _bedrock_converse_messages_pt function in litellm/litellm_core_utils/prompt_templates/factory.py to handle empty assistant content by replacing it with a non-empty placeholder text.

Key Changes:

1. String content handling (line 3833): Replace empty or whitespace-only strings with "."
2. List content handling (line 3807): Replace empty text elements in content lists with "."

Code Changes

# Before
text_content = element["text"] if element["text"].strip() else "."
assistant_content.append(BedrockContentBlock(text=text_content))

# After  
text_content = _assistant_content if _assistant_content.strip() else "."
assistant_content.append(BedrockContentBlock(text=text_content))

Screenshot

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Project	Deployment	Preview	Comments	Updated (UTC)
litellm	Ready	Preview	Comment	Oct 23, 2025 5:12pm

[ishaan-jaff]

lgtm