Fix task configuration with None context parameter in YAML

[devin-ai-integration]

Fix task configuration with None context parameter in YAML

Summary

Fixes #3696 - Tasks can now be configured with context: None in YAML without causing a KeyError.

Root Cause: When context: None is specified in YAML configuration files, yaml.safe_load() converts it to the string 'None' instead of Python's None object. The existing code attempted to iterate over this string character by character ('N', 'o', 'n', 'e'), causing a KeyError: 'N' when trying to look up task names.

The Fix: Added an isinstance(context_list, list) check in crew_base.py:_map_task_variables() before iterating the context list. This ensures only actual list values are processed, while None and other non-list values are silently ignored (the task's context remains unset).

Changes:

• Modified src/crewai/project/crew_base.py to add type check before iterating context
• Added test case test_task_with_none_context_from_yaml with test configurations in tests/config_none_context/
• Test verifies both context: None case and valid context list case work correctly

Review & Testing Checklist for Human

⚠️ Important: I was unable to test this locally due to a corrupted uv.lock file in the development environment. Please verify:

• Run the new test locally - Verify test_task_with_none_context_from_yaml passes and actually reproduces the original issue when the fix is reverted
• Test with real crew configuration - Create a simple crew with a task that has context: None in YAML and verify it works end-to-end
• Regression testing - Verify existing crews with valid context lists (e.g., context: [task1, task2]) still work correctly
• Edge case testing - Consider testing other non-list context values (e.g., context: null, context: "", context: 123) to ensure they don't cause crashes

Suggested Test Plan

1. Clone the PR branch locally
2. Run uv run pytest tests/test_project.py::test_task_with_none_context_from_yaml -vv
3. Create a minimal crew with YAML config containing context: None and run it
4. Run the full test suite to check for regressions: uv run pytest tests -vv

Notes

• The isinstance check is defensive and handles any non-list value, not just the string 'None'
• This follows existing patterns in the codebase for optional parameters
• Link to Devin run: https://app.devin.ai/sessions/f55f24ce6283444db0e1252191a34980
• Requested by: João (joao@crewai.com)

[devin-ai-integration]

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