code: public void process(IntermediateForm form) throws IOException {
      if (form.deleteList.size() > 0) {
        deleteList.addAll(form.deleteList);
      }
  
      if (form.dir.sizeInBytes() > 0) {
        if (writer == null) {
          writer = createWriter();
        }
  
        writer.addIndexesNoOptimize(new Directory[] { form.dir });
        numDocs++;
      }
  
    }
docs: This method is used by the index update combiner and process an
  intermediate form into the current intermediate form. More specifically,
  the input intermediate forms are a single-document ram index and/or a
  single delete term.
  @param form  the input intermediate form
  @throws IOException