title: Skip processing in Pipeline If argument met
body: <p>I'm grabbing product info from a site and checking o see if it's in stock and shippable or not.  If it's out of stock o not available to ship then I don't care about adding it to my database.  So, I have the item and it's makes its way to the pipeline and once I see that it's out of stock or doesn't ship I just want to quit processing it in the pipeline and dump everything I have on it and go back to the spider to grab the next item to be processed.  I hope that makes since.  I tried the raise DropItem() but nothing happened.  I checked the DB and when that field is empty it should be skipping it right?  Here's the code.</p>
  
  <pre><code>Ships = item['Ships']
  Stock = item['InStock']
  if "shipping not available" in Ships[0].lower():
      raise DropItem()
  if len(Stock) is 0:
      raise DropItem ("Test")
  if "instock" not in Stock[0].lower():
      raise DropItem()
  </code></pre>
  
  <p>I've tested the output of the code and it's working correctly as far as the if statement goes.  It's just not working when I get to the THEN part. So, to summarize one of the examples in there, When len(Stock) is 0 then I want to stop processing this particular item and move on to getting and processing the next item.</p>