abhigyanpatwari/GitNexus · error · ValueError

task {task['id']} field {field} must be a string

Error message

task {task['id']} field {field} must be a string

What it means

Raised by select_tasks after the required-string check passes. The optional fields ref and setup (optional_strings at runner_tasks.py:32) must be strings if present. Unlike the required fields, blank/whitespace-only is permitted here — only the str type is enforced.

Source

Thrown at eval/workflow_bench/runner_tasks.py:42

def select_tasks(tasks: list[Any], *, include_expensive: bool) -> tuple[list[dict[str, Any]], list[str]]:
    """Validate task metadata and filter opt-in expensive scenarios."""

    selected: list[dict[str, Any]] = []
    skipped: list[str] = []
    seen: set[str] = set()
    required_strings = ("id", "class", "repo", "prompt", "verify")
    optional_strings = ("ref", "setup")
    for index, raw_task in enumerate(tasks):
        if not isinstance(raw_task, Mapping):
            raise ValueError(f"task {index} must be a mapping")
        task = dict(raw_task)
        for field in required_strings:
            if not isinstance(task.get(field), str) or not task[field].strip():
                raise ValueError(f"task {index} requires a nonblank string {field}")
        for field in optional_strings:
            if field in task and not isinstance(task[field], str):
                raise ValueError(f"task {task['id']} field {field} must be a string")
        task_id = task["id"]
        if not re.fullmatch(r"[A-Za-z0-9][A-Za-z0-9._-]{0,127}", task_id):
            raise ValueError(f"task id must be a simple artifact-safe slug: {task_id!r}")
        if task_id in seen:
            raise ValueError(f"duplicate task id: {task_id}")
        seen.add(task_id)
        expensive = task.get("expensive", False)
        if not isinstance(expensive, bool):
            raise ValueError(f"task {task_id} expensive metadata must be boolean")
        copies = task.get("sandbox_copy", [])
        if not isinstance(copies, list) or not all(isinstance(path, str) and path for path in copies):
            raise ValueError(f"task {task_id} sandbox_copy must be a string list")
        dependencies = task.get("sandbox_dependencies", [])
        if not isinstance(dependencies, list):
            raise ValueError(f"task {task_id} sandbox_dependencies must be a list")
        for dependency in dependencies:
            if (
                not isinstance(dependency, Mapping)

View on GitHub (pinned to d540b00184)

Solutions

1. Inspect the offending task's ref/setup value and confirm it is a scalar string.
2. If you need no ref/setup, remove the key entirely rather than leaving it null.
3. Quote the value in YAML to avoid implicit type coercion.

Example fix

# before
- id: t1
  ref:
    - main
# after
- id: t1
  ref: main

OPTIONAL = ("ref", "setup")
for i, t in enumerate(doc.get("tasks", [])):
    for f in OPTIONAL:
        if f in t and not isinstance(t[f], str):
            raise SystemExit(f"task {i} field {f} must be a string")

def optional_fields_are_strings(task: dict) -> bool:
    return all(
        f not in task or isinstance(task[f], str)
        for f in ("ref", "setup")
    )

When it happens

Trigger: A task sets ref to a YAML list (e.g. a multi-line block folded wrong) or to a number, or sets setup to null/mapping. The check is `field in task and not isinstance(task[field], str)`.

Common situations: Writing `ref: HEAD` works but `ref: [HEAD]` does not; `setup:` with no value yields None and trips it; an automated task generator emitting setup as an object.

Related errors

• task {index} requires a nonblank string {field}
• task {task_id} expensive metadata must be boolean
• task {task_id} sandbox_copy must be a string list
• task {task_id} sandbox_dependencies must be a list
• task id must be a simple artifact-safe slug: {task_id!r}

AI-assisted analysis of abhigyanpatwari/GitNexus@d540b00184 (2026-08-12). Data as JSON: /api/errors/5863e037f144d0ab. Report an issue: GitHub.