private static String digits(long val, int digits) {
        long hi = 1L << (digits * 4);
        return Long.toHexString(hi | (val & (hi - 1))).substring(1);
    }
Returns a {@link UUID#toString()} string without dashes.

@param uuid the uuid
@return the string form
helper/src/main/java/me/lucko/helper/utils/UndashedUuids.java