Error !

AttributeError: 'NoneType' object has no attribute 'url'

% if article._file('images'): <img class="teaser-image" src="${ article._file('images').url('listitem')}" alt=""/> % else: <img class="teaser-image" src="${object._file('default-img').url('listitem')}" alt="" /> % endif </div> <div class="bottom-part"> <h2 class="title">${article.val("title")}</h2> <div class="teaser">
templates/default/news, line 28:
<img class="teaser-image" src="${object._file('default-img').url('listitem')}" alt="" />
templates/default/site, line 129:
%>
/srv/dd-web03/limecms/verge/verge01/local/lib/python2.7/site-packages/mako/runtime.py, line 890:
callable_(context, *args, **kwargs)
/srv/dd-web03/limecms/verge/verge01/local/lib/python2.7/site-packages/mako/runtime.py, line 864:
_exec_template(inherit, lclcontext, args=args, kwargs=kwargs)
/srv/dd-web03/limecms/verge/verge01/local/lib/python2.7/site-packages/mako/runtime.py, line 829:
**_kwargs_for_callable(callable_, data))
/srv/dd-web03/limecms/verge/verge01/local/lib/python2.7/site-packages/mako/template.py, line 445:
return runtime._render(self, self.callable_, args, data)
/var/limecms/verge/verge01/verge-inst/Products/LimeTemplate/LimeTemplate.py, line 702:
html = mytemplate.render(object=object, site=site, request=self.REQUEST, extra=extra.get('kwargs', None), **extra)