code: function (dataType) {
          var task = getCurrentTask(this);
          if (task) {
              var data = task.context.data;
              return dataType == null ? data : data.getLinkedData(dataType);
          }
          else {
              // When series is not alive (that may happen when click toolbox
              // restore or setOption with not merge mode), series data may
              // be still need to judge animation or something when graphic
              // elements want to know whether fade out.
              return inner(this).data;
          }
      }
docs: Consider some method like `filter`, `map` need make new data,
  We should make sure that `seriesModel.getData()` get correct
  data in the stream procedure. So we fetch data from upstream
  each time `task.perform` called.
  @param {string} [dataType]
  @return {module:echarts/data/List}