code: @Override
    public int advance(int target) throws IOException {
      docId = NO_MORE_DOCS;
      currentStartPosition = NO_MORE_POSITIONS;
      currentEndPosition = NO_MORE_POSITIONS;
      return docId;
    }
docs: /*
  (non-Javadoc)
  
  @see org.apache.lucene.search.DocIdSetIterator#advance(int)