Fixed concurrency issue on multiple files upload

        File file = path.toFile();

        /**

         * This block must be synchronized, to avoid concurrency issues when

         * multiple files are uploaded to a new folder in parallel.

         */

        synchronized (this) {

            if (!file.getParentFile().exists()) {

                if (!file.getParentFile().mkdirs()) {

                    throw new IllegalStateException("Unable to create parent folder: " + file.getParentFile().getAbsolutePath());

                }

            }

        }

        Files.copy(is, file.toPath());

    }