code: function handleData(state, data) {
      debug('Read data from ', streamName(this));
  
      try {
        addData.call(state, data);
      } catch (err) {
        debug(`Error adding data from ${streamName(this)}`, err);
        reject(err);
        done();
        return;
      }
  
      if (options.incremental) {
        doCompare(options.incremental, CompareType.incremental);
      }
    }
docs: Handles data read from the stream for a given state.
  @private