Good question. My first approach has been to just port the implementation in https://github.com/akvo/akvo-flow/blob/feature/point-updates-v4/GAE/src/org/waterforpeople/mapping/app/web/SurveyManagerServlet.java#L172

Although I agree your proposal is cleaner, if we take that path the parser will need to be modified, java's `split` method will not include the empty string in the result, ending up in a smaller array.
The current solution is just storing `null` in the database. That value is never read, as the monitoring features capabilities are not enabled in any group.