What's the best way to make a sublist entry field on a suitelet mandatory? Is using validateLine on a CS that's attached to the the suitelet the best way? The field allows the user to update the reporting month on the record, but we want to make sure it's not blank

Is that supposed to work in a sublist? I was hoping it would be that simple, but it didn't seem to work. The way the suitelet works is we enter some criteria and then it brings up a list of results and in the list of results a couple of the columns are text fields. These have a client script attached so the edits they make will flow back to the custom record.