Joan focused on enhancing the organization and test coverage of Empty instances within the typelevel/cats repository during February 2025. She refactored the Empty.fromEmptyK implementation by introducing a new trait, EmptyInstances2, which improved the maintainability and clarity of the codebase. To ensure correctness, Joan added comprehensive tests, including testOptionEmpty, to verify Empty instances for nested type constructors. Her work leveraged functional programming principles and Scala, emphasizing robust type safety and modular design. While the scope was limited to a single feature, the depth of the refactor laid a solid foundation for future enhancements and improved long-term code quality.