long nextCheckTimeNs() {
        if (overloadCircuitBreaker.isOverload()) {
            return Long.MAX_VALUE;
        } else {
            return nextCheckTimeNs0();
        }
    }
Check if the oldest broker to have heartbeated has already violated the
sessionTimeoutNs timeout and needs to be fenced.

@return      An Optional broker node id.
metadata/src/main/java/org/apache/kafka/controller/BrokerHeartbeatManager.java