code: public File save(final String filename, final Serializer serializer) {
          File file = serializer.save(this, filename);
          if (log != null) //noinspection ConstantConditions
              log.info("Reflections successfully saved in " + file.getAbsolutePath() + " using " + serializer.getClass().getSimpleName());
          return file;
      }
docs: serialize to a given directory and filename using given serializer
  <p>* it is preferred to specify a designated directory (for example META-INF/reflections),
  so that it could be found later much faster using the load method