Worked on stabilizing certificate handling in the JetBrainsRuntime repository by addressing a critical bug in X509 extension access. Focused on hardening the X509CertImpl.getExtensionValue method to prevent NullPointerExceptions when certificate information or extensions are missing, thereby improving the resilience of certificate parsing and validation workflows. Introduced CertExtensions.java to rigorously validate getExtensionValue and getKeyUsage under various extension presence scenarios, ensuring robust unit testing coverage. Utilized Java for development, with an emphasis on API design, security, and X.509 certificate handling. The work enhanced the safety and reliability of certificate operations without introducing new features, concentrating on targeted bug resolution.