protected TopicAdmin createAdmin(TopicAdmin existing) {
        if (closed.get()) {
            throw new ConnectException("The " + this + " has already been closed and cannot be used.");
        }
        if (existing != null) {
            return existing;
        }
        return factory.apply(adminProps);
    }
Method used to create a {@link TopicAdmin} instance. This method must be side-effect free, since it is called from within
the {@link AtomicReference#updateAndGet(UnaryOperator)}.

@param existing the existing instance; may be null
@return the
connect/runtime/src/main/java/org/apache/kafka/connect/util/SharedTopicAdmin.java