docs: public void setParentGroup(String parentGroup) {
  
          if (CmsStringUtil.isEmpty(parentGroup) || parentGroup.equals("null") || parentGroup.equals("none")) {
              parentGroup = null;
          }
          if (parentGroup != null) {
              try {
                  getCms().readGroup(parentGroup);
              } catch (CmsException e) {
                  throw new CmsIllegalArgumentException(e.getMessageContainer());
              }
          }
          m_parentGroup = parentGroup;
      }