docs: @Override
      public void add(final int index, final SyndCategory obj) {
          final SyndCategoryImpl sCat = (SyndCategoryImpl) obj;
          DCSubject subject;
          if (sCat != null) {
              subject = sCat.getSubject();
          } else {
              subject = null;
          }
          subjects.add(index, subject);
      }