BrokersToIsrs.PartitionsOnReplicaIterator partitionsWithBrokerInElr(int brokerId) {
        Map<Uuid, int[]> topicMap = elrMembers.get(brokerId);
        if (topicMap == null) {
            topicMap = Collections.emptyMap();
        }
        return new BrokersToIsrs.PartitionsOnReplicaIterator(topicMap, false);
    }
Update our records of a partition's ELR.

@param topicId       The topic ID of the partition.
@param partitionId   The partition ID of the partition.
@param prevElr       The previous ELR, or null if the partition is new.
@param nextElr       The new ELR, or null if the partition is being removed.
metadata/src/main/java/org/apache/kafka/controller/BrokersToElrs.java