Sei Shinagawa contributed to the flexeval repository by addressing a critical issue in the ROUGE metric evaluation pipeline. He implemented robust edge-case handling in Python to prevent ValueError exceptions when model outputs were empty or contained only punctuation, which previously caused instability in automated evaluation runs. By refining the data processing logic, he ensured that metric reporting remained consistent and reliable, supporting downstream machine learning workflows. This targeted bug fix, co-authored with Shun Kiyono, improved the overall resilience of the evaluation process. The work demonstrated careful attention to detail and a solid understanding of both Python and evaluation metric design.