@Override
    @JsonProperty("max_number_of_indices")
    public abstract int maxNumberOfIndices();
@Test
    public void testDeserialization() throws IOException {
        final ObjectMapper objectMapper = new ObjectMapperProvider().get();
        final String json = "{ \"type\": \"org.graylog2.indexer.retention.strategies.DeletionRetentionStrategyConfig\", \"max_number_of_indices\": 23}";
        final RetentionStrategyConfig config = objectMapper.readValue(json, RetentionStrategyConfig.class);

        assertThat(config).isInstanceOf(DeletionRetentionStrategyConfig.class);
        assertThat(((DeletionRetentionStrategyConfig) config).maxNumberOfIndices()).isEqualTo(23);
    }