Error !

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

image = object.get(image.get('sql')) %> <li> <img src="${image.url(dontfollow=True)}/slider" alt="${image.val('title')}" /> </li> % endfor </ul> </div> <div id="carousel" class="twelve columns alpha flexslider">
memory:0x7f9a7e9775d0, line 46:
<img src="${image.url(dontfollow=True)}/slider" alt="${image.val('title')}" />
templates/ferd/site, line 150:
${self.main_content()}
/var/limecms/ferd/ferd01/local/lib/python2.7/site-packages/Mako-0.8.0-py2.7.egg/mako/runtime.py, line 841:
callable_(context, *args, **kwargs)
/var/limecms/ferd/ferd01/local/lib/python2.7/site-packages/Mako-0.8.0-py2.7.egg/mako/runtime.py, line 815:
_exec_template(inherit, lclcontext, args=args, kwargs=kwargs)
/var/limecms/ferd/ferd01/local/lib/python2.7/site-packages/Mako-0.8.0-py2.7.egg/mako/runtime.py, line 783:
**_kwargs_for_callable(callable_, data))
/var/limecms/ferd/ferd01/local/lib/python2.7/site-packages/Mako-0.8.0-py2.7.egg/mako/template.py, line 443:
return runtime._render(self, self.callable_, args, data)
/var/limecms/ferd/ferd01/ferd-inst/Products/LimeTemplate/LimeTemplate.py, line 679:
html = mytemplate.render(object=object, site=site, **extra)