Worked on the google/j2cl repository to address a subtle issue in the HashMap implementation, specifically refining the computeIfAbsent method to handle null keys consistently. The solution ensured that when a null key is provided, the method now reliably returns the newly added value, aligning behavior with expected Java semantics and reducing the risk of runtime inconsistencies. This update was reinforced by introducing a targeted regression test, which validates the correct handling of null-key scenarios and guards against future regressions. The work demonstrated proficiency in Java development, HashMap internals, and unit testing, focusing on robustness and long-term code reliability.