@Override
  public boolean areInSameZone(InternalDistributedMember member1,
      InternalDistributedMember member2) {

    if (!redundancyZones.isEmpty()) {
      String zone1 = redundancyZones.get(member1);
      String zone2 = redundancyZones.get(member2);
      return zone1 != null && zone1.equals(zone2);
    } else {
      return areOnEquivalentHost(member1, member2);
    }
  }
This is an event reflecting that a InternalDistributedMember may be missing but has not yet
left the system.
geode-core/src/main/java/org/apache/geode/distributed/internal/ClusterDistributionManager.java