@Override
  public KnownVersion[] getSerializationVersions() {
    return null;
  }
A LeaveRequestMessage is sent by a member of the cluster when it intends to shut down.
This informs other members of the cluster that they should not consider the shutdown to
be abnormal. No response is required.
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/messages/LeaveRequestMessage.java