Jannes Koehler focused on backend development and mocking for the univelop/yust repository, dedicating the month to improving the reliability of the mocked data layer rather than adding new features. He addressed a critical null-access bug in the mocked database service by introducing null checks before accessing nested JSON path segments, which reduced runtime errors and improved test stability. Working primarily with Dart, Jannes enhanced the robustness of data retrieval in test environments, ensuring safer and more predictable outcomes. His work demonstrated a thoughtful approach to error handling and contributed to more reliable automated testing workflows within the project’s backend infrastructure.