public synchronized ZooKeeper getZooKeeper() {
    // Callers expect an initialized ZooKeeper instance
    // Pre HBASE-28529 the constructor used to call checkZk()
    try {
      return checkZk();
    } catch (Exception x) {
      LOG.warn("Failed to initialize Zookeeper object, returning null", x);
      return null;
    }
  }
Returns the wrapped ZooKeeper client. If the wrapped client hasn't been created yet then tries
create it first.
@return the wrapped ZK client of null if the creation has failed.
hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/RecoverableZooKeeper.java