Elements not always present on page

[ghost]

I use:

class ProductPage(Item):
      coupon = Attr('.coupon', 'title')

However some product pages do not contain the coupon html
so they fail with

  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/htmlparsing.py", line 79, in parse
    return element.css(self.selector)[0].attrs[self.attr]
IndexError: list index out of range

What's the best practice to deal with that situation?