Usage of loki absent_over_time function for grafana alert

I am using Grafana 8.3.2 and Loki 2.5.0.I need to setup an Grafana alert using the loki function absent_over_time() for a log statement when it is present between a time frame. I can see the function returning blank visually when the statement is present, but it doesn’t return a value to be used for check in the alert. Currently I see min,max,last,sum,count,median,diff,diff_abs,percent_dff,percent_diff_abs,count_not_null in Grafana alert options but not sure which one can be used with absent_over_time to achieve my requirement. Can anyone please let me know how to use this and share me a working query.