In September 2025, Andrii Klepchiiev worked on the opensearch-project/k-NN repository, focusing on backend development and bug fixing in Java. He addressed a critical issue in the k-NN search functionality, where a null 'k' parameter was incorrectly treated as zero, leading to inaccurate filter results. Andrii implemented a solution that correctly handles null or empty 'k' values, ensuring accurate query outcomes. He reinforced the fix with comprehensive backward compatibility and parameter handling tests, and updated the changelog to document the change. His work improved the reliability and stability of the API, demonstrating depth in testing and backend engineering.