During December 2024, Changyi contributed to the alibaba/fastjson2 repository, focusing on enhancing the correctness and stability of JSON serialization in Java. He addressed two critical bugs by refining the application of ToStringSerializer for Integer and Long types, ensuring accurate string representations and improving client interoperability. Changyi also increased the minimum buffer capacity in JSONWriterUTF8.writeStringEscaped to better handle escaped characters, reducing the risk of runtime errors. His work included developing targeted unit tests to verify these changes, demonstrating a methodical approach to bug fixing, robust JSON processing, and a commitment to maintaining high code quality and reliability.