@Override
    public String toString() {
        return "(name=" + name +
                ", numPartitions=" + numPartitions.map(String::valueOf).orElse("default") +
                ", replicationFactor=" + replicationFactor.map(String::valueOf).orElse("default") +
                ", replicasAssignments=" + replicasAssignments +
                ", configs=" + configs +
                ")";
    }
The configuration for the new topic or null if no configs ever specified.
clients/src/main/java/org/apache/kafka/clients/admin/NewTopic.java