docs: private static boolean isSolrSpellcheckIndexDirectoryEmpty() {
  
          final File path = new File(getSolrSpellcheckRfsPath());
          final File[] directories = path.listFiles(SPELLCHECKING_DIRECTORY_NAME_FILTER);
  
          // Each directory that has been created by Solr but hasn't been indexed yet
          // contains exactly two files. If there are more files, at least one index has
          // already been built, so return false in that case.
          if (directories != null) {
              for (final File directory : directories) {
                  if (directory.list().length > 2) {
                      return false;
                  }
              }
          }
          return true;
      }