@Override
    public String toString() {
        return "admin client for brokers at " + bootstrapServers();
    }
Close the underlying {@link TopicAdmin} instance, if one has been created, and prevent new ones from being created.

<p>Once this method is called, the {@link #get()} and {@link #topicAdmin()} methods,
nor any previously returned {@link TopicAdmin} instances may be used.

@param timeout the maximum time to wait while the underlying admin client is closed; may not be null
connect/runtime/src/main/java/org/apache/kafka/connect/util/SharedTopicAdmin.java