private Map<byte[], String> foo(String v1, String v2) {
        if (v1.length() == v2.length()) {
            Map<byte[], String> map = new HashMap<>();
            byte[] key = v1.getBytes();
            map.put(key, v1);
            System.arraycopy(v2.getBytes(), 0, key, 0, v2.length());
            map.put(key, v2);
            return map;
        }
        return null;
    }