code: private void mergeWithSmoosher() throws IOException
    {
      // Get processed elements from the stack and write.
      List<File> fileToProcess = new ArrayList<>(completedFiles);
      completedFiles = new ArrayList<>();
      for (File file : fileToProcess) {
        add(file);
        if (!file.delete()) {
          LOG.warn("Unable to delete file [%s]", file);
        }
      }
    }
docs: Merges temporary files created by delegated SmooshedWriters on to the main
  smoosh file.
  
  @throws IOException