@Override
  public List<ID> getRecipients() {
    if (getMulticast()) {
      return (List<ID>) Collections.singletonList(ALL_RECIPIENTS);
    } else if (recipients != null) {
      return recipients;
    } else {
      return (List<ID>) Collections.singletonList(ALL_RECIPIENTS);
    }
  }
AbstractGMSMessage is the superclass of most Membership messages. These messages
may be sent via the Messenger service or via a TcpClient.

@param <ID>
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/messages/AbstractGMSMessage.java