code: private synchronized void initQueryBuilder() throws IOException {
          if (queryBuilder == null) {
              indexReader = DirectoryReader.open(indexDirectory);
              indexSearcher = new IndexSearcher(indexReader);
              queryBuilder = new QueryBuilder(writer.getAnalyzer());
          }
      }
docs: Performs a delayed initialization of the query builder to ensure that the index has been
  fully created.
  
  @throws IOException Unspecified IO exception.