@Override
  public void addToResults(InternalDistributedMember member, Set<PersistentID> persistentIds) {
    if (persistentIds != null) {
      getResults().put(member, persistentIds);
    }
  }
AbortBackupStep overrides addToResults in order to include members with empty persistentIds
(such as the sender).
geode-core/src/main/java/org/apache/geode/internal/cache/backup/AbortBackupStep.java