title: How to choose what to be written to the back-end with Celery?
body: <p>I am using Celery for a web-scraping project I have. And sometimes the URLs in the queue will be duplicates. That is why the task function returns None if it has seen this URL.
  How to stop <strong>Celery</strong> from writing a result to the result backend if the value is None or any other value that I don't like?</p>