code: public void addOptionalField(String optionalField) {
          if (optionalField == null) {
              return;
          } else if (this.optionalFields == null) {
              this.optionalFields = new ArrayList<String >();
          }
          this.optionalFields.add(optionalField);
      }
docs: Add a field to the list of optional fields that are included in the inventory results.