handle falsy values correctly in merge logic

[gnunneley]

Description

The source + target merge process does not handle falsy values (false, 0, etc.) properly and does not merge/adds warnings when a source value is falsy. See added test which fails on main.

Type of Change

• [x] Bug Fix
• [ ] New Feature
• [ ] Breaking Change
• [ ] Refactor
• [ ] Documentation
• [ ] Other (please describe)

Checklist

• [x] I have read the contributing guidelines
• [x] Existing issues have been referenced (where applicable)
• [x] I have verified this change is not present in other open pull requests
• [ ] Functionality is documented
• [x] All code style checks pass
• [x] New code contribution is covered by automated tests
• [x] All new and existing tests pass