public Set<AlertTargetEntity> getAlertTargets() {
    if( null == alertTargets ) {
      return Collections.emptySet();
    }

    return Collections.unmodifiableSet(alertTargets);
  }
Gets an immutable set of the targets that will receive notifications for
alert definitions in this group.

@return the targets that will be dispatch to for alerts in this group, or
        an empty set if there are none (never {@code null}).
ambari-server/src/main/java/org/apache/ambari/server/orm/entities/AlertGroupEntity.java