@Override
    public void close() {
        keySerializer.close();
    }
The serializer that is used for {@link TimestampedKeyAndJoinSide}, which is a combo key format of <timestamp, left/right flag, raw-key>
@param <K> the raw key type
streams/src/main/java/org/apache/kafka/streams/state/internals/TimestampedKeyAndJoinSideSerializer.java