'Return a :term:`URL` to the masthead image for this issue or `None`.
By default it returns the value of the member `self.masthead_url` which
is normally `None`. If you want your recipe to download a masthead for the e-book
override this method in your subclass, or set the member variable `self.masthead_url`
before this method is called.
Masthead images are used in Kindle MOBI files.'

def get_masthead_url(self):

    return getattr(self, 'masthead_url', None)
