code: public Decision addDecision(SoftwareSystem softwareSystem, String id, Date date, String title, DecisionStatus status, Format format, String content) {
          checkIdIsSpecified(id);
          checkTitleIsSpecified(title);
          checkContentIsSpecified(content);
          checkDecisionStatusIsSpecified(status);
          checkFormatIsSpecified(format);
          checkDecisionIsUnique(softwareSystem, id);
  
          Decision decision = new Decision(softwareSystem, id, date, title, status, format, content);
          this.decisions.add(decision);
  
          return decision;
      }
docs: Adds a new decision to this workspace.
  
  @param softwareSystem    the SoftwareSystem to associate the decision with
  @param id                the ID of the decision
  @param date              the date of the decision
  @param title             the title of the decision
  @param status            the status of the decision
  @param format            the format of the decision content
  @param content           the content of the decision
  @return  a Decision object