During May 2025, Taekyu Kim enhanced the Club domain model in the Recruiting-Your-Club/ryc repository by focusing on immutability and safer object initialization. He refactored Java code to enforce final fields and locals, removing mutable setters to reduce runtime errors and simplify future maintenance. By leveraging the Builder Pattern and @Builder.Default, he ensured that collection fields in the Club model are initialized to empty lists by default, preventing NullPointerExceptions. This work, rooted in object-oriented programming and careful refactoring, improved the robustness and maintainability of the codebase while introducing minimal behavioral changes, enabling safer and more predictable future development.