Worked on the microsoft/presidio repository to address a critical bug in the Custom Operator’s validation process. Focused on backend development using Python, the solution involved moving return-type enforcement from the validate() method to the operate() method, ensuring that user-supplied lambdas are only invoked with real data and return the expected string type. This approach resolved issues with stateful lambdas that previously encountered errors due to premature invocation with dummy values. Emphasizing robust error handling and unit testing, the fix improved operator reliability and data integrity, reducing runtime errors and enhancing developer confidence in production pipeline behavior without introducing new features.