public String bootstrapServers() {
        return adminProps.getOrDefault(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, "<unknown>").toString();
    }
Get the string containing the list of bootstrap server addresses to the Kafka broker(s) to which
the admin client connects.

@return the bootstrap servers as a string; never null
connect/runtime/src/main/java/org/apache/kafka/connect/util/SharedTopicAdmin.java