fix: CrewOutput.json raises IndexError instead of ValueError on empty tasks_output

[chuenchen309]

Problem

CrewOutput.json does self.tasks_output[-1].output_format != ... before checking whether the list is empty, so an empty tasks_output (a genuine, reachable state — constructed directly elsewhere in this test suite, e.g. test_crew.py's kickoff_for_each_async mocks) raises a raw IndexError instead of the intended, documented ValueError one line below.

Fix

Guard with not self.tasks_output or ... before indexing.

Testing

• New file lib/crewai/tests/test_crew_output.py: asserts the empty-tasks_output case raises ValueError (not IndexError), plus a sanity check that a non-empty, JSON-output final task still returns the dumped JSON.
• Confirmed red→green: reverting only crew_output.py reproduces IndexError: list index out of range; reapplying passes.
• Full test_crew_output.py + test_crew.py: 133 passed, 1 skipped (unrelated).
• ruff check and mypy — clean.
• xref: no open PR touches crew_output.py.

AI-Generated disclosure

Drafted with Claude Code and personally reviewed/tested before submission. Per CONTRIBUTING.md's llm-generated label requirement: as an external contributor I don't have permission to self-apply GitHub labels (confirmed via gh pr edit --add-label, GraphQL permission error) — disclosing here instead; happy to have a maintainer apply the label if needed.

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ℹ️ Recent review info

⚙️ Run configuration

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Run ID: be378798-4b14-44b8-bff6-18b3829e88de

📥 Commits

Reviewing files that changed from the base of the PR and between 0e5d0ec and 4efeeab.

📒 Files selected for processing (2)

• lib/crewai/src/crewai/crews/crew_output.py
• lib/crewai/tests/test_crew_output.py

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📝 Walkthrough

Walkthrough

Changes

CrewOutput JSON handling

Layer / File(s)	Summary
JSON output validation and tests lib/crewai/src/crewai/crews/crew_output.py, lib/crewai/tests/test_crew_output.py	CrewOutput.json checks for empty task outputs before accessing the final task, raises ValueError when no JSON output exists, and returns serialized JSON for a JSON-formatted final task. Tests cover both behaviors.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: preventing IndexError and restoring the intended ValueError for empty tasks_output.
Description check	✅ Passed	The description is directly related to the change and explains the bug, fix, and testing performed.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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