Init with AtomicReference

    private static final AtomicReference<Map<String, File>> templates = new AtomicReference<>();

    private static Map<String, File> getTemplatesMap() {
        Map<String, File> map = templates.get();
        if (map == null) {
            Collection<File> files = VisualDesignerPluginUtil.getFiles(
                    VaadinDesignerConstants.TEMPLATE_FOLDER, "html");

            map = new LinkedHashMap<String, File>(files.size());
            for (File file : files) {
                map.put(FilenameUtils.getBaseName(file.getName()), file);
            }
            // templates could be already filled by the separate thread, so
            // previous work could be not needed, but it's rare and there is no
            // any thread race condition.
            if (templates.compareAndSet(null, map)) {
                return map;
            } else {
                return templates.get();
            }
        } else {
            return map;
        }
    }