title: Scrapy Error: 'NotSupported: Unsupported URL scheme '': no handler available for that scheme'
body: <p>I am trying to scrap a site but while running the script, I'm getting following error</p>
  
  <blockquote>
    <p>'NotSupported: Unsupported URL scheme '': no handler available for
    that scheme'</p>
  </blockquote>
  
  <p>If the rule is not wrong, why does it occur and what's your suggestion, please help me. Thanks a lot.</p>
  
  <p>code is here:</p>
  
  <pre><code>from scrapy.spiders import CrawlSpider, Rule, BaseSpider
  from scrapy.linkextractors import LinkExtractor 
  class FellowSearch(CrawlSpider):
      name ='fellow'
      allowed_domains = ['emma.cam.ac.uk']
      start_urls = [' https://www.emma.cam.ac.uk/']
  
      rules =(Rule(LinkExtractor(allow=(r'\?id=\d+$')),callback='parse_obj', follow=True),)
  
      def parse_obj(self, response):
          print response.url
  </code></pre>