@Override
 public Object removing(int index, Paired<BlockParser, Block> paired) {
   Block block = paired.getSecond();
   if (block != null) nodeClassifier.remove(block);
   return paired;
 }
 @Override
 public void adding(int index, Paired<BlockParser, Block> paired, Object v) {
   Block block = paired.getSecond();
   if (block != null) nodeClassifier.add(block);
 }