Worked on the alibaba/fastjson2 repository to enhance the robustness of its JSON parsing logic by introducing strict input validation. Addressed issue 3883 by implementing defensive checks that prevent malformed or illegal input from causing crashes or incorrect error handling during parsing. Developed comprehensive unit tests in Java to verify the parser’s behavior with edge-case and invalid inputs, ensuring regression safety and improved reliability. Focused on aligning the parsing pathway with quality and security standards, the work emphasized careful validation and thorough test coverage. Utilized skills in Java, JSON parsing, and unit testing to deliver a targeted and maintainable fix.