code: function (query, callback) {
      if (!callback) {
        callback = query;
        query = null;
      }
  
      if (typeof query === 'string') {
        query = { aggregateId: query };
      }
  
      var self = this;
  
      this.store.getLastEvent(query, function (err, evt) {
        if (err) return callback(err);
  
        callback(null, new EventStream(self, query, evt ? [evt] : []));
      });
    }
docs: loads the last event in a stream
  @param {Object || String} query    the query object [optional]
  @param {Function}         callback the function that will be called when this action has finished
  `function(err, eventstream){}`