code: @Override
     public int nextDoc() throws IOException
     {
        if (nextDoc == NO_MORE_DOCS)
        {
           return nextDoc;
        }
  
        nextDoc = docFilter.nextSetBit(nextDoc + 1);
        if (nextDoc < 0)
        {
           nextDoc = NO_MORE_DOCS;
        }
        return nextDoc;
     }
docs: {@inheritDoc}