@SuppressWarnings("WEAK_MESSAGE_DIGEST_MD5")
    @Override
    public Object convert(String value) {
        if (value == null || value.isEmpty()) {
            return value;
        }

        // MessageDigest is not threadsafe. #neverForget
        return DigestUtils.md5Hex(value);
    }
@Test
    public void testConvert() throws Exception {
        Converter hc = new HashConverter(new HashMap<String, Object>());

        assertNull(hc.convert(null));
        assertEquals("", hc.convert(""));
        assertEquals("c029b5a72ae255853d7151a9e28c6260", hc.convert("graylog2"));
    }