Unable to create Kafka Redis Sink with Single Message Transformations

I am trying to create a Kafka Redis sink that deletes a particular key in Redis. One of the ways is to create a Record or Message in Kafka with a specific key and Value as null. But as per the use case, generating the keys is not possible. As a workaround, I wrote a Single message transformer that takes the message from Kafka, sets a particular Key, and sets Value equals null.

Here are my Kafka Connect Confgurations

"connector.class": "com.github.jcustenborder.kafka.connect.redis.RedisSinkConnector","transforms.invalidaterediskeys.type": "com.github.cjmatta.kafka.connect.smt.InvalidateRedisKeys","redis.database": "0","redis.client.mode": "Standalone","topics": "test_redis_deletion2","tasks.max": "1","redis.hosts": "REDIS-HOST","key.converter": "org.apache.kafka.connect.storage.StringConverter","transforms": "invalidaterediskeys"}

Here is the code for the transformations :

public class InvalidateRedisKeys<R extends ConnectRecord<R>> implements Transformation<R> {    private static final Logger LOG = LoggerFactory.getLogger(InvalidateRedisKeys.class);    private static final ObjectMapper mapper = new ObjectMapper()            .configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);    @Override    public ConfigDef config() {        return new ConfigDef();    }    @Override    public void configure(Map<String, ?> settings) {    }    @Override    public void close() {    }    @Override    public R apply(R r) {        try {            return r.newRecord(                    r.topic(),                    r.kafkaPartition(),                    Schema.STRING_SCHEMA,                    getKey(r.value()),                    null,                    null,                    r.timestamp()            );        } catch (IOException e) {            LOG.error("a.jsonhandling.{}", e.getMessage());            return null;        } catch (Exception e) {            LOG.error("a.exception.{}", e.getMessage());            return null;        }    }    private String getKey(Object value) throws IOException {        A a = mapper.readValue(value.toString(), A.class);        long userId = a.getUser_id();        int roundId = a.getRound_id();        return KeyGeneratorUtil.getKey(userId, roundId);    }}

where A is

public class A {    private long user_id;    private int round_id;}

And KeyGeneratorUtil contains a static function that generates a relevant string and sends the results.

I took help from

1. https://github.com/cjmatta/kafka-connect-insert-uuid
2. https://github.com/apache/kafka/tree/trunk/connect/transforms/src/main/java/org/apache/kafka/connect/transforms

When I try to initialize Kafka Connect, it says invalid Configurations. Is there something that I am missing?