What causes "result is None for {job_id = }" in windmill-labs/windmill?

Have the script return an explicit value (e.g. `return {...}`).

windmill-labs/windmill · error · Exception

result is None for {job_id = }

Error message

result is None for {job_id = }

What it means

get_result() fetches a completed job's result; if assert_result_is_not_none=True and the raw response text is None it raises this error. Note the check is on result.text being None, which is rare — an empty body usually yields '' not None — so this mainly fires when the HTTP layer returns a null body object.

Source

Thrown at python-client/wmill/wmill/client.py:576

    def get_result(
        self,
        job_id: str,
        assert_result_is_not_none: bool = True,
    ) -> Any:
        """Get the result of a completed job.

        Args:
            job_id: UUID of the completed job
            assert_result_is_not_none: Raise exception if result is None

        Returns:
            Job result
        """
        result = self.get(f"/w/{self.workspace}/jobs_u/completed/get_result/{job_id}")
        result_text = result.text
        if assert_result_is_not_none and result_text is None:
            raise Exception(f"result is None for {job_id = }")
        try:
            return result.json()
        except JSONDecodeError:
            return result_text

    def get_variable(self, path: str) -> str:
        """Get a variable value by path.

        Args:
            path: Variable path in Windmill

        Returns:
            Variable value as string
        """
        path = parse_variable_syntax(path) or path
        if self.mocked_api is not None:
            variables = self.mocked_api["variables"]
            try:

View on GitHub (pinned to e474e8803c)

Solutions

Have the script return an explicit value (e.g. `return {...}`).
Set assert_result_is_not_none=False when a None result is valid.
Check the job's result on the runs page to confirm what was stored.

Example fix

// before
res = client.get_result(job_id, assert_result_is_not_none=True)
// after
res = client.get_result(job_id, assert_result_is_not_none=False)
if res is None:
    res = {}

Defensive patterns

Strategy: validation

Validate before calling

completed = client.get_job(job_id)
if completed.get('result') is None and assert_non_none:
    raise ValueError(f'job {job_id} has no result; do not assert')

Type guard

def result_present(res) -> bool:
    return res is not None and res != ''

Try / catch

try:
    res = client.get_result(job_id, assert_result_is_not_none=True)
except Exception as e:
    if 'result is None' in str(e):
        res = None
    else:
        raise

Prevention

Ensure scripts return explicit values before querying their results.
Only enable assert_result_is_not_none when the script contract guarantees output.
Check the run's result in the UI to confirm stored output shape.

When it happens

Trigger: Calling get_result(job_id, assert_result_is_not_none=True) on a job whose completed result payload is empty/None (e.g. script returned nothing).

Common situations: Side-effect-only scripts that return no value; querying results before the job produced output; asserting non-None on jobs known to return null.

Related errors

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/15154a7162281d57. Report an issue: GitHub.