During December 2024, Changyi contributed to the alibaba/fastjson2 repository by focusing on enhancing the correctness and stability of JSON serialization in Java. He addressed two critical bugs, refining the ToStringSerializer logic to ensure Integer and Long types were consistently serialized as strings, which improved 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 and regression prevention while deepening the robustness of JSON processing and serialization workflows.