code: public PubsubFuture<Topic> getTopic(final String canonicalTopic) {
      validateCanonicalTopic(canonicalTopic);
      return get("get topic", canonicalTopic, readJson(Topic.class));
    }
docs: Get a Pub/Sub topic.
  
  @param canonicalTopic The canonical (including project) name of the topic to get.
  @return A future that is completed when this request is completed. The future will be completed with {@code null}
  if the response is 404.