code: function (aggregateId, callback) {
      if (!aggregateId || !_.isString(aggregateId)) {
        var err = new Error('Please pass a valid aggregateId!');
        debug(err);
        throw err;
      }
      if (!callback || !_.isFunction(callback)) {
        var err = new Error('Please pass a valid callback!');
        debug(err);
        throw err;
      }
  
      var self = this;
  
      this.aggregateLock.getAll(aggregateId, function (err, workerIds) {
        if (err) {
          return callback(err);
        }
  
        if (workerIds.length === 1 && workerIds[0] === self.id) {
          return callback(null);
        }
  
        var err = new ConcurrencyError('Aggregate is locked by an other command handler!');
        debug(err);
        callback(err);
      });
    }
docs: Checks if the aggregate lock is ok.
  @param {String}   aggregateId The passed aggregateId.
  @param {Function} callback    The function, that will be called when this action is completed.
  `function(err){}`