Null wrapUpCode in /api/v2/analytics/details queries

Is there a specific filter I’m missing to get actual values for wrapUpCode in the detail queries, or is this data just not exposed via the API? I’m hitting /api/v2/analytics/details/conversations with the groupBy set to wrapUpCode, but every row returns null for that field. The JSON payload looks correct otherwise. It’s gotta be a query error.