code: public void populate() {
      PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
      try {
        Resource[] bootstrap3Themes = resolver.getResources(LOCAL_CSS_BOOTSTRAP_3_THEME_LOCATION);
        Resource[] bootstrap4Themes = resolver.getResources(LOCAL_CSS_BOOTSTRAP_4_THEME_LOCATION);
  
        // filter out themes already stored in the database
        List<Resource> newThemes =
            Arrays.stream(bootstrap3Themes)
                .filter(
                    theme ->
                        dataService.getRepository(STYLE_SHEET).findOneById(theme.getFilename())
                            == null)
                .collect(Collectors.toList());
  
        newThemes.forEach(
            nt -> {
              try {
                addNewTheme(nt, bootstrap4Themes);
              } catch (IOException | MolgenisStyleException e) {
                LOG.error("error adding new bootstrap themes", e);
              }
            });
  
      } catch (IOException e) {
        LOG.error("error populating bootstrap themes", e);
      }
    }
docs: Populate the database with the available bootstrap themes found in the jar. This enables the
  release of the application with a set of predefined bootstrap themes.
  
  <p>If a given bootstrap 3 theme is located a matching bootstrap 4 theme is added the the
  styleSheet row is present.