code: @Override
      public SyndCategory set(final int index, final SyndCategory obj) {
          final SyndCategoryImpl sCat = (SyndCategoryImpl) obj;
          DCSubject subject;
          if (sCat != null) {
              subject = sCat.getSubject();
          } else {
              subject = null;
          }
          subject = subjects.set(index, subject);
          if (subject != null) {
              return new SyndCategoryImpl(subject);
          } else {
              return null;
          }
      }
docs: Sets a category in an existing position in the list.
  <p>
  
  @param index position to set the category.
  @param obj the SyndCategoryImpl object to set.
  @return the SyndCategoryImpl object that is being replaced, <b>null</b> if none.