public void reset(@Nullable List<T> newOriginalItems) {
   if (newOriginalItems != null) {
     originalItems.clear();
     originalItems.addAll(newOriginalItems);
   }
   modifiedToOriginal.clear();
   originalToModified.clear();
 }
 @Override
 public void clear() {
   super.clear();
   blockCount = 0;
   term_blocks.clear();
 }