public PartitionedRegion removeShadowPR(String fullpath) {
    try {
      sender.getLifeCycleLock().writeLock().lock();
      sender.setEnqueuedAllTempQueueEvents(false);
      return userRegionNameToShadowPRMap.remove(fullpath);
    } finally {
      sender.getLifeCycleLock().writeLock().unlock();
    }
  }
This returns queueRegion if there is only one PartitionedRegion using the GatewaySender
Otherwise it returns null.
geode-core/src/main/java/org/apache/geode/internal/cache/wan/parallel/ParallelGatewaySenderQueue.java