def scrape(self, request, response, link_type=None):
        '''Iterate the scrapers, returning the first of the results.'''
        for scraper in self._document_scrapers:
            scrape_result = scraper.scrape(request, response, link_type)

            if scrape_result is None:
                continue

            if scrape_result.link_contexts:
                return scrape_result
Iterate the scrapers, returning the first of the results.