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