Worked on the prometheus/prometheus repository, focusing on backend development with Go to enhance the stability of PromQL evaluation. Addressed a runtime reliability issue by fixing a nil pointer dereference in the DurationExpr.PositionRange method, which previously caused panics when the right-hand side was nil. The solution involved implementing a fallback to the left-hand side’s position range, ensuring correct handling of duration expressions and preventing crashes in production environments. This work demonstrated careful defensive programming and code quality practices, leveraging static analysis tools and aligning with related fixes to maintain consistency and robustness in the codebase. No new features were added.