code: @Override
    public void close() throws IOException {
      delegateFieldsProducer.close();
      for (Entry<String, IndexInput> entry : indexInputList.entrySet()) {
        entry.getValue().close();
      }
    }
docs: /*
  (non-Javadoc)
  
  @see org.apache.lucene.codecs.FieldsProducer#close()