public static Gson instance() {
        return SingletonHolder.INSTANCE;
    }
@Test
    void rejectsSerializationOfAESEncrypter() {
        final IllegalArgumentException e = assertThrows(IllegalArgumentException.class, () ->
                Serialization.instance().toJson(new AESEncrypter(mock(AESCipherProvider.class))));
        assertEquals(format("Refusing to serialize a %s instance and leak security details!", AESEncrypter.class.getName()), e.getMessage());
    }