private void verifyDistributionManagerCanProcessMessage() {
    if (!(dm instanceof ClusterDistributionManager)) {
      throw new IllegalArgumentException(
          "Processing of AlertListenerMessage requires ClusterDistributionManager instead of "
              + dm.getClass().getSimpleName());
    }
  }
Remove verifyDistributionManagerCanProcessMessage when
{@link AlertListenerMessage#process(ClusterDistributionManager)} no longer requires
ClusterDistributionManager.
geode-core/src/main/java/org/apache/geode/alerting/internal/ClusterAlertMessaging.java