fix(agents): keep null in the task output schema embedded in the prompt

[monkscode]

build_task_prompt_with_schema embeds the task output schema into the prompt using
generate_model_description, whose strip_null_types defaults to True. Combined with
ensure_all_properties_required, an Optional[str] = None field is presented to the
model as a required, non-nullable string — leaving it no way to express "not
applicable", and contradicting the provider-side response schema generated from the
same model.

That sanitizer targets OpenAI strict function-calling schemas. This call site produces
prompt prose, where those constraints do not apply.

This passes strip_null_types=False, matching the existing call for tool schemas at
utilities/agent_utils.py:268. required still lists every property, which is the
standard strict-mode idiom once the type is nullable.

Before / after

For class Step(BaseModel): name: str; note: Optional[str] = None:

before   note: {"default": null, "type": "string"}                              <- cannot be null
after    note: {"anyOf": [{"type": "string"}, {"type": "null"}], "default": null}

required is ['name', 'note'] in both cases — unchanged by this PR.

Tests

Adds lib/crewai/tests/agents/test_agent_utils.py. No existing test referenced
build_task_prompt_with_schema, so the file is new; maintainers may prefer it
elsewhere. It fails on main with KeyError: 'anyOf' and passes with this change.

Existing cassette-based tests are unaffected: vcr_config matches on
["method", "scheme", "host", "port", "path"], not on the request body.

Fixes #6774

[coderabbitai]

📝 Walkthrough

Walkthrough

The task prompt schema now preserves null types for JSON and Pydantic outputs. Tests verify that optional Pydantic fields produce schemas accepting both strings and null values.

Changes

Nullable task output schemas

Layer / File(s)	Summary
Schema generation and nullable-field validation lib/crewai/src/crewai/agent/utils.py, lib/crewai/tests/agents/test_agent_utils.py	build_task_prompt_with_schema passes strip_null_types=False when generating JSON and Pydantic schemas. Tests verify that optional fields retain an anyOf schema for string and null values.

Suggested reviewers: lorenzejay

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: preserving null values in task output schemas embedded in prompts.
Description check	✅ Passed	The description directly explains the schema bug, the fix, the expected behavior, and the added tests.
Linked Issues check	✅ Passed	The changes implement issue #6774 by preserving nullable optional fields and adding tests for the generated prompt schema.
Out of Scope Changes check	✅ Passed	The code and test changes are limited to the linked issue objectives and contain no unrelated scope.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

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• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (2)

lib/crewai/tests/agents/test_agent_utils.py (2)

25-27: 🗄️ Data Integrity & Integration | 🔵 Trivial | ⚡ Quick win

Cover the output_json branch.

This test constructs Task with output_pydantic only. It never executes the task.output_json branch changed in build_task_prompt_with_schema. Add a matching JSON-output case or parameterize the test over both output attributes.

Based on PR objectives: nullable prompt schemas must be preserved for both JSON and Pydantic outputs.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@lib/crewai/tests/agents/test_agent_utils.py` around lines 25 - 27, Extend the
test around build_task_prompt_with_schema to cover Task configured with
output_json in addition to output_pydantic, either by adding a matching
JSON-output case or parameterizing both configurations. Ensure the assertions
verify nullable prompt schemas are preserved for both output attributes.

---

33-36: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Make the anyOf assertion order-independent.

The exact list comparison makes member order part of the test contract. JSON Schema alternatives are order-independent, so a valid generator change can fail this test.

Proposed assertion

-    assert schema["properties"]["note"]["anyOf"] == [
-        {"type": "string"},
-        {"type": "null"},
-    ]
+    assert {
+        entry["type"] for entry in schema["properties"]["note"]["anyOf"]
+    } == {"string", "null"}

Based on coding guidelines: tests should focus on behavior rather than implementation details.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@lib/crewai/tests/agents/test_agent_utils.py` around lines 33 - 36, Update the
`anyOf` assertion in the agent schema test to compare alternatives without
relying on list order, while still requiring exactly the string and null schema
members. Preserve the existing validation of the `note` property’s schema.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@lib/crewai/tests/agents/test_agent_utils.py`:
- Around line 25-27: Extend the test around build_task_prompt_with_schema to
cover Task configured with output_json in addition to output_pydantic, either by
adding a matching JSON-output case or parameterizing both configurations. Ensure
the assertions verify nullable prompt schemas are preserved for both output
attributes.
- Around line 33-36: Update the `anyOf` assertion in the agent schema test to
compare alternatives without relying on list order, while still requiring
exactly the string and null schema members. Preserve the existing validation of
the `note` property’s schema.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: fe8f54e9-1bab-4281-b4e9-a21ba24e21be

📥 Commits

Reviewing files that changed from the base of the PR and between c8f441c and 4ca325a.

📒 Files selected for processing (2)

• lib/crewai/src/crewai/agent/utils.py
• lib/crewai/tests/agents/test_agent_utils.py