BerriAI/litellm · error · ValueError

At least one message is required for A2A completion

Error message

At least one message is required for A2A completion

What it means

Error "At least one message is required for A2A completion" thrown in BerriAI/litellm.

Source

Thrown at litellm/llms/a2a/chat/transformation.py:216

    ) -> dict:
        """
        Transform OpenAI request to A2A JSON-RPC 2.0 format.

        Args:
            model: Model name
            messages: List of OpenAI messages
            optional_params: Optional parameters
            litellm_params: LiteLLM parameters
            headers: Request headers

        Returns:
            A2A JSON-RPC 2.0 request dict
        """
        # Generate request ID
        request_id: Final = str(uuid.uuid4())

        if not messages:
            raise ValueError("At least one message is required for A2A completion")

        # Convert all messages to maintain conversation history
        # Use helper to format conversation with role prefixes
        full_context: Final = convert_messages_to_prompt(messages)

        # Create single A2A message with full conversation context
        a2a_message: Final = {
            "role": "user",
            "parts": [{"kind": "text", "text": full_context}],
            "messageId": str(uuid.uuid4()),
        }

        # Build JSON-RPC 2.0 request
        # For A2A protocol, the method is "message/send" for non-streaming
        # and "message/stream" for streaming
        stream: Final = optional_params.get("stream", False)
        method: Final = "message/stream" if stream else "message/send"

View on GitHub (pinned to 6c2dcb801b)

Solutions

1. Pass at least one message in the A2A completion request.

When it happens

Trigger: Thrown at litellm/llms/a2a/chat/transformation.py:216 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of BerriAI/litellm@6c2dcb801b (2026-08-15). Data as JSON: /api/errors/478524f55201fac8. Report an issue: GitHub.