Nicola Cabiddu refactored the ExpressionContext core in the percona/percona-server-mongodb repository, focusing on maintainability and correct parameter passing. Using C++ and object-oriented design principles, Nicola consolidated configuration and operational data into ExpressionContextParams, removing duplicate members and streamlining the expression evaluation process. This approach ensured that all necessary parameters were correctly propagated and accessible, reducing the risk of future errors and enabling safer, more reliable refactors. The work improved testability and future extensibility by centralizing data management, reflecting a thoughtful application of code cleanup and refactoring skills to enhance the reliability of query expression evaluation paths.