code: public void setLineItem(com.google.api.ads.admanager.axis.v201902.LineItem lineItem) {
          this.lineItem = lineItem;
      }
docs: Sets the lineItem value for this ProspectiveLineItem.
  
  @param lineItem   * The target of the forecast. If {@link LineItem#id} is null
  or no line item exists with that ID,
  then a forecast is computed for the subject, predicting
  what would happen if it were added
  to the network. If a line item already exists with
  {@link LineItem#id}, the forecast is
  computed for the subject, predicting what would happen
  if the existing line item's settings
  were modified to match the subject.