What causes ""Mem0Middleware requires a non-empty `user_id`."" in agentscope-ai/agentscope?

Pass a concrete non-empty string id, e.g. user_id='user-123'

agentscope-ai/agentscope · error · ValueError

"Mem0Middleware requires a non-empty `user_id`."

Error message

"Mem0Middleware requires a non-empty `user_id`."

What it means

Mem0Middleware namespaces all memory operations by user_id; a None or whitespace-only string has no valid namespace, so the constructor rejects it immediately.

Source

Thrown at src/agentscope/middleware/_longterm_memory/_mem0/_middleware.py:254

                the agent that created them. When ``False`` search uses
                ``user_id`` only, so a user's memories are shared across
                agents.
            await_write:
                When ``True`` (default) the post-turn ``add`` call is
                awaited inline. When ``False`` it's fire-and-forget —
                faster response but exceptions only surface in logs.
            memory_section_header, memory_section_intro:
                Strings used when injecting retrieved memories into
                the model's messages list (``static_control`` /
                ``both`` modes).
            tool_instructions:
                Markdown block appended to the agent's system prompt
                in ``agent_control`` / ``both`` modes, advertising the
                ``search_memory`` / ``add_memory`` tools to the LLM.
        """
        is_empty_user_id = isinstance(user_id, str) and not user_id.strip()
        if user_id is None or is_empty_user_id:
            raise ValueError(
                "Mem0Middleware requires a non-empty `user_id`.",
            )
        if mode not in ("static_control", "agent_control", "both"):
            raise ValueError(
                f"Unknown mode {mode!r}; expected one of "
                f"'static_control', 'agent_control', 'both'.",
            )

        client = self._resolve_client(
            client=client,
            chat_model=chat_model,
            embedding_model=embedding_model,
            mem0_config=mem0_config,
        )
        self._client = client

        self._user_id = user_id
        self._agent_id = agent_id

View on GitHub (pinned to e90f1c7592)

Solutions

Pass a concrete non-empty string id, e.g. user_id='user-123'
When deriving from sessions, default it: user_id = session_user or 'anonymous'
Strip and check the value before constructing the middleware

Example fix

// before
mw = Mem0Middleware(user_id=get_user(request))
// after
uid = get_user(request) or f'anon-{request.client}'
mw = Mem0Middleware(user_id=uid)

Defensive patterns

Strategy: validation

Validate before calling

if user_id is None or (isinstance(user_id, str) and not user_id.strip()):
    raise ValueError('user_id required')
# or normalize:
user_id = (user_id or '').strip() or 'anonymous'

Type guard

def is_valid_user_id(uid) -> bool:
    return isinstance(uid, str) and bool(uid.strip())

Try / catch

try:
    mw = Mem0Middleware(user_id=uid, ...)
except ValueError as e:
    if 'user_id' in str(e):
        mw = Mem0Middleware(user_id='anonymous', ...)
    else:
        raise

Prevention

Never pass session-derived ids unchecked; default them
Unit-test middleware construction with empty-string user_id

When it happens

Trigger: Mem0Middleware(user_id='') or user_id=' ' or omitting user_id (default None); passing a dynamically computed id that came back empty.

Common situations: Deriving user_id from request headers/session objects that are missing in dev; copy-pasted examples without filling in the id.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of agentscope-ai/agentscope@e90f1c7592 (2026-08-28). Data as JSON: /api/errors/4ab10d08a77ae6fb. Report an issue: GitHub.