code: public com.google.api.ads.admanager.axis.v201902.HistoricalAdjustment getHistoricalAdjustment() {
          return historicalAdjustment;
      }
docs: Gets the historicalAdjustment value for this TrafficForecastAdjustmentSegment.
  
  @return historicalAdjustment   * The content of the adjustment which references historical data.
  This field should be set if
  {@code basisType} is {@link BasisType.HISTORICAL}
  and null if {@link BasisType.ABSOLUTE}.