docs: private Map<UUID, DateTime> getNextTransitionsForSubscriptions(final BillingEventSet billingEvents) {
  
          final DateTime now = clock.getUTCNow();
          final Map<UUID, DateTime> result = new HashMap<UUID, DateTime>();
          for (final BillingEvent evt : billingEvents) {
              final UUID subscriptionId = evt.getSubscriptionId();
              final DateTime evtEffectiveDate = evt.getEffectiveDate();
              if (evtEffectiveDate.compareTo(now) <= 0) {
                  continue;
              }
              final DateTime nextUpcomingPerSubscriptionDate = result.get(subscriptionId);
              if (nextUpcomingPerSubscriptionDate == null || nextUpcomingPerSubscriptionDate.compareTo(evtEffectiveDate) > 0) {
                  result.put(subscriptionId, evtEffectiveDate);
              }
          }
          return result;
      }