private void stopReceivers() {
    Set<GatewayReceiver> receivers = getCache().getGatewayReceivers();
    for (GatewayReceiver receiver : receivers) {
      receiver.stop();
    }
  }
Since the sender is attached to a region and in use, it can not be destroyed. Hence, exception
is thrown by the sender API.
geode-wan/src/distributedTest/java/org/apache/geode/internal/cache/wan/serial/SerialGatewaySenderOperationsDistributedTest.java