openai/openai-python · error · ValueError

Expected a non-empty value for `message_id` but received {me

Error message

Expected a non-empty value for `message_id` but received {message_id!r}

What it means

client.beta.threads.messages.retrieve() also requires a non-empty message_id for the GET /threads/{thread_id}/messages/{message_id} path. It is validated after thread_id, so you only see this error when thread_id is valid but message_id is empty/None.

Source

Thrown at src/openai/resources/beta/threads/messages.py:149

        extra_body: Body | None = None,
        timeout: float | httpx2.Timeout | None | NotGiven = not_given,
    ) -> Message:
        """
        Retrieve a message.

        Args:
          extra_headers: Send extra headers

          extra_query: Add additional query parameters to the request

          extra_body: Add additional JSON properties to the request

          timeout: Override the client-level default timeout for this request, in seconds
        """
        if not thread_id:
            raise ValueError(f"Expected a non-empty value for `thread_id` but received {thread_id!r}")
        if not message_id:
            raise ValueError(f"Expected a non-empty value for `message_id` but received {message_id!r}")
        extra_headers = {"OpenAI-Beta": "assistants=v2", **(extra_headers or {})}
        return self._get(
            path_template("/threads/{thread_id}/messages/{message_id}", thread_id=thread_id, message_id=message_id),
            options=make_request_options(
                extra_headers=extra_headers,
                extra_query=extra_query,
                extra_body=extra_body,
                timeout=timeout,
                security={"bearer_auth": True},
            ),
            cast_to=Message,
        )

    @typing_extensions.deprecated("The Assistants API is deprecated in favor of the Responses API")
    def update(
        self,
        message_id: str,
        *,

View on GitHub (pinned to 9917c6e28e)

Solutions

Pass the message's id: client.beta.threads.messages.retrieve(thread_id=tid, message_id=message.id)
Double-check argument order and that the value is the id string
Validate externally sourced ids before the call

Example fix

# before
client.beta.threads.messages.retrieve(thread_id=tid, message_id="")
# after
client.beta.threads.messages.retrieve(thread_id=tid, message_id=message.id)

Defensive patterns

Strategy: type-guard

Validate before calling

if not (isinstance(message_id, str) and message_id):
    raise ValueError("message_id must be a non-empty string")

Type guard

def is_message_id(v: object) -> bool:
    return isinstance(v, str) and v.startswith("msg_") and len(v) > 4

Prevention

Pass message.id, never the Message object
Use keyword arguments to avoid positional mix-ups

When it happens

Trigger: Calling retrieve with a valid thread_id but message_id="" or None — commonly passing the whole Message object or the thread id by mistake in the second argument.

Common situations: Argument-order mix-ups (message_id=thread_id), ids from truncated logs/URLs, or deserialized records missing the message id.

Understand the failure class

Background: Missing required parameter errors: what 'X is required' and 'the required X param is missing' mean, and how to fix them — this error's family across 27 libraries.

Related errors

AI-assisted analysis of openai/openai-python@9917c6e28e (2026-08-28). Data as JSON: /api/errors/d2394f2611168e0b. Report an issue: GitHub.