<!-- (you don't have to strictly follow this form) --> **Use case** When there is no event during specific window, current behavior of Proton can't emit that window. It ends up a bit weird semantic results. **Describe the solution you'd like** Take reference from ClickHouse: https://clickhouse.com/blog/working-with-time-series-data-and-functions-ClickHouse **Describe alternatives you've considered** <!-- A clear and concise description of any alternative solutions or features you've considered. --> **Additional context** <!-- Add any other context or screenshots about the feature request here. -->