Google doesn't guarantee that we'll always have relevant ads to display, because ad serving depends on a number of factors, including our ability to crawl your site, your web page content and the availability of relevant Google ads.
Similarly, if Google doesn't have ads for an AdSense for search query, or if the query will return non-family-safe ads, we won't show any ads.
If we don't have relevant ads for a given web page, or if we haven't yet crawled your site, we'll display no ads.