title: How to set the default value of an Item.Field() in Scrapy?
body: <p>I'm trying to scrape a website which does not display the same data from page to page. I'd like my spider to return a default value for each attribute it could not scrape. I know that this could be done in the item declaration like this :</p>
  
  <pre><code>class MyItem(scrapy.Item):
       myfield = scrapy.Field(default='NULL')
  </code></pre>
  
  <p>However, this method seems not to work anymore (I'm using Scrapy 1.3.0). If I try to export this particular field when the value has not been found I got :</p>
  
  <pre><code>KeyError: 'myfield'
  </code></pre>
  
  <p>Is there a workaround?</p>