Fix Flow initialization with Pydantic models having required fields

[devin-ai-integration]

Fix Flow initialization with Pydantic models having required fields

Summary

Fixes issue #3629 where Flow initialization would fail with a ValidationError when using Pydantic state models that have required (non-optional) fields.

Root Cause: The _create_initial_state() method was instantiating state models without any arguments (state_type()), causing Pydantic validation to fail for required fields.

Solution: Modified _create_initial_state() to accept a kwargs parameter and pass it to all state model instantiation points. Also removed the redundant _initialize_state(kwargs) call from __init__() since kwargs are now handled during initial state creation.

Key Changes:

• Updated _create_initial_state() method signature to accept optional kwargs
• Modified all 4 state instantiation paths to use **(kwargs or {})
• Removed redundant _initialize_state(kwargs) call from Flow.__init__()
• Added 5 comprehensive tests covering required fields, optional fields, mixed scenarios, and backward compatibility

Review & Testing Checklist for Human

• Verify backward compatibility: Test existing Flows with FlowState subclasses still work without providing kwargs
• Test the original issue: Create a Flow with a Pydantic state having required fields and confirm it works with provided kwargs
• Check edge cases: Test mixed required/optional fields, default value overrides, and that id auto-generation still works properly
• Run full test suite: Ensure no regressions in existing Flow functionality across the codebase

Recommended Test Plan

1. Create a simple Flow with required Pydantic fields (name: str, age: int) and verify it works: MyFlow(name="test", age=25)
2. Test an existing Flow that uses FlowState subclasses to ensure no regression
3. Test a Flow with mixed required/optional fields to verify defaults work correctly

Notes

• All 30 existing tests in test_flow.py pass, plus 5 new tests added
• The fix maintains the existing API - users just need to provide values for required fields when creating Flow instances
• Link to Devin run: https://app.devin.ai/sessions/df894da7ac744e97a5f1d7184c45d7a2
• Requested by: João ([email protected]) via Slack

[devin-ai-integration]

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