MemPalace/mempalace · error · ValueError

{field_name} must be a non-empty string

Error message

{field_name} must be a non-empty string

What it means

Raised by sanitize_name() when the wing/room/entity name is not a string, or is a string that is empty or whitespace-only after potential stripping. Names become directory/collection identifiers, so a blank name would create an unusable path. Every MCP write tool and most CLI write paths route names through this validator.

Source

Thrown at mempalace/config.py:79

    The same rule is applied by ``init`` when persisting `topics_by_wing`
    and when writing `mempalace.yaml`, so the miner's lookup matches at
    mine time regardless of the source dirname.

    Leading/trailing separators are stripped so a path-encoded dirname like
    ``-home-user-proj`` yields ``home_user_proj`` rather than a leading-
    underscore slug that ``sanitize_name`` (and thus the MCP write tools)
    would reject.
    """
    return name.lower().replace(" ", "_").replace("-", "_").strip("_")


def sanitize_name(value: str, field_name: str = "name") -> str:
    """Validate and sanitize a wing/room/entity name.

    Raises ValueError if the name is invalid.
    """
    if not isinstance(value, str) or not value.strip():
        raise ValueError(f"{field_name} must be a non-empty string")

    value = value.strip()

    if len(value) > MAX_NAME_LENGTH:
        raise ValueError(f"{field_name} exceeds maximum length of {MAX_NAME_LENGTH} characters")

    # Block path traversal
    if ".." in value or "/" in value or "\\" in value:
        raise ValueError(f"{field_name} contains invalid path characters")

    # Block null bytes
    if "\x00" in value:
        raise ValueError(f"{field_name} contains null bytes")

    # Enforce safe character set
    if not _SAFE_NAME_RE.match(value):
        raise ValueError(f"{field_name} contains invalid characters")

View on GitHub (pinned to 06cb6987f0)

Solutions

1. Supply a real, non-empty name for the field identified in the message (field_name tells you which argument)
2. In calling code, check the value before the call: if not (isinstance(n, str) and n.strip())
3. Fix shell scripts to fail fast on unset variables (set -u / ${NAME:?})

Example fix

# before
wing = os.environ.get("WING", "")   # empty when unset
create_wing(wing)

# after
wing = os.environ["WING"]           # fails fast, or validate first
if not wing.strip(): raise SystemExit("WING name required")
create_wing(wing)

# Before any name-taking call:
if not isinstance(name, str) or not name.strip():
    raise SystemExit("name must be a non-empty string")

def is_valid_name(value) -> bool:
    return isinstance(value, str) and bool(value.strip())

try:
    safe = sanitize_name(name, "wing")
except ValueError as exc:
    if "non-empty" in str(exc):
        name = fallback_name  # e.g. "unnamed"
    else:
        raise

When it happens

Trigger: Calling a write tool or CLI command with name=None, name=123 (non-string), name="" or name=" " — e.g. a script passing an unset environment variable or an LLM tool call omitting the name field so it arrives as empty.

Common situations: Unset shell variable expanding to empty string ($NAME with NAME undefined); MCP client sending null for an omitted optional-looking field; whitespace-only name pasted from a form; programmatic callers passing an int id.

Related errors

• {field_name} exceeds maximum length of {MAX_NAME_LENGTH} cha
• {field_name} contains invalid path characters
• {field_name} contains null bytes
• {field_name} contains invalid characters
• pass inline text or a file, not both

AI-assisted analysis of MemPalace/mempalace@06cb6987f0 (2026-08-15). Data as JSON: /api/errors/80d91a94ceddc301. Report an issue: GitHub.