@Override
    public String toString() {
        return "ProducerIdsBlock(" +
                "assignedBrokerId=" + assignedBrokerId +
                ", firstProducerId=" + firstProducerId +
                ", size=" + blockSize +
                ')';
    }
Get the first ID of the next block following this one.
server-common/src/main/java/org/apache/kafka/server/common/ProducerIdsBlock.java