docs: function ensureLock(client, path) {
    var lock = client.lock;
    if(!(lock && !('unlocked' in lock))) {
      // Create an error so we get a stack, too.
      var err = new Error('Attempted sync step without lock.');
      log.error({client: client, err: err}, 'Client should own lock but does not for ' + path);
      return false;
    }
    return true;
  }