Worked on the micronaut-projects/micronaut-core repository, focusing on improving the reliability of API query parameter parsing. Addressed a bug affecting single-value query parameters when using the @Format("csv") annotation, ensuring correct handling across CSV, SSV, and pipe-delimited formats. The solution involved refining the parsing logic in the backend and introducing comprehensive regression tests to validate behavior and prevent future issues. Utilized Groovy and Java to implement and test these changes, emphasizing correctness and robust test coverage. This work enhanced API stability by preventing invalid query values from reaching clients, contributing to a more predictable developer experience and reliable backend services.