For schools that have the School Settings option Calculate Attendance Totals Based on Period Attendance enabled, this produces a Value cannot be null error while dropping a student from attendance using the Update Attendance button on the Demographics page or when adding a Leave record on the Attendance Enrollment page.
This option, on occasion, can also cause the Monthly Attendance Summary reports to fail.
A workaround is to uncheck the Calculate Attendance Totals Based on Period Attendance option on the School Settings page to allow a student to be dropped from attendance or to run the Monthly Summary reports.
A fix is currently being worked on and we will update this post when an update is released.
The following Aeries Idea has also been created to keep users updated. https://ideas.aeries.com/forums/926386/suggestions/42278215