code: public void process(DocumentAndOp doc, Analyzer analyzer) throws IOException {
      if (doc.getOp() == DocumentAndOp.Op.DELETE
          || doc.getOp() == DocumentAndOp.Op.UPDATE) {
        deleteList.add(doc.getTerm());
  
      }
  
      if (doc.getOp() == DocumentAndOp.Op.INSERT
          || doc.getOp() == DocumentAndOp.Op.UPDATE) {
  
        if (writer == null) {
          // analyzer is null because we specify an analyzer with addDocument
          writer = createWriter();
        }
  
        writer.addDocument(doc.getDocument(), analyzer);
        numDocs++;
      }
  
    }
docs: This method is used by the index update mapper and process a document
  operation into the current intermediate form.
  @param doc  input document operation
  @param analyzer  the analyzer
  @throws IOException