Filter rows that are not shared between two tables

I have MatrixTables for two cohorts, and I would like to find the rows that are in one or the other but not both. I converted them both into Tables and did an outer join, so now I have all of the rows in one table with empty entries if a row was present only in one table. The issue is, I’m not sure how to find those empty entries and extract those rows into a new table. Any help would be appreciated.