code: public Stat exists(String path, boolean watch) throws KeeperException,
              InterruptedException {
          verbotenThreadCheck();
          return exists(path, watch ? watchManager.defaultWatcher : null);
      }
docs: Return the stat of the node of the given path. Return null if no such a
  node exists.
  <p>
  If the watch is true and the call is successful (no exception is thrown),
  a watch will be left on the node with the given path. The watch will be
  triggered by a successful operation that creates/delete the node or sets
  the data on the node.
  
  @param path
  the node path
  @param watch
  whether need to watch this node
  @return the stat of the node of the given path; return null if no such a
  node exists.
  @throws KeeperException
  If the server signals an error
  @throws InterruptedException
  If the server transaction is interrupted.