@Override
      public JsonDeserializer<?> findMapDeserializer(MapType type, DeserializationConfig config, BeanDescription beanDesc, KeyDeserializer keyDeserializer, TypeDeserializer elementTypeDeserializer, JsonDeserializer<?> elementDeserializer) throws JsonMappingException {
        if (IS_BSON_TYPE.test(type)) {
          Codec<?> codec = findCodecOrNull(registry, type.getRawClass());
          return codec == null ? null : deserializer(codec);
        }
        return null;
      }
Create {@link CodecRegistry} adapter on the top of existing mapper instance
criteria/mongo/src/org/immutables/criteria/mongo/bson4jackson/JacksonCodecs.java