Fix ValidationError on BooleanField with None value

[craigds]

Fixes #13

Summary

• Catch ValidationError during field change detection
• Skip invalid fields (like deferred fields)
• Add tests for BooleanField with None value

Details

When models with non-nullable BooleanField are instantiated with None values (as Django admin does), field.to_python() raises ValidationError. This wraps the call in try-except to skip invalid fields during change detection, similar to how deferred fields are handled.

Test Plan

• All 16 tests pass
• Ruff linting passes
• Mypy type checking passes

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Created with Claude Code

[Copilot]

Pull request overview

This PR fixes a crash that occurs when Django models with non-nullable BooleanFields are instantiated with None values, which commonly happens in Django admin forms before user input. The fix wraps the field.to_python() call in a try-except block to gracefully handle ValidationError exceptions by skipping invalid fields during change detection.

• Adds exception handling for ValidationError in field change detection
• Implements tests for BooleanField with None values
• Ensures invalid fields are skipped similar to deferred fields

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
fieldsignals/signals.py	Adds try-except block around field.to_python() to catch ValidationError and skip fields with invalid values, preventing crashes during change detection
fieldsignals/tests/test_signals.py	Adds BooleanField test class and two test cases: one verifying that post_init doesn't crash with None values, and another testing field transitions from invalid to valid states

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