Error !

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

<ul> % for item in leftmenu: <li class="${['','active'][item.active]}"> <a href="${item.object.url()}">${item.object.val('title')}</a> <% submenu = [] submenu = item.object.getMenuItems() %> % if submenu != [] and item.active:
/var/limecms/nmh/nmh01/nmh-inst-01/Products/LimeVirtualObject/LimeVirtualObject.py, line 86:
szurl = object.url()
/var/limecms/nmh/nmh01/nmh-inst-01/Products/LimeAPI/LimeCore.py, line 890:
url = self._url(lang='%s' % langcode)
templates/nmhresp/menu/menus, line 303:
<a href="${item.object.url()}">${item.object.val('title')}</a>
templates/nmhresp/site, line 246:
${menus.renderLeftMenu(object, True)}
/srv/ddnmh01/limecms/nmh/nmh01/local/lib/python2.7/site-packages/mako/runtime.py, line 899:
callable_(context, *args, **kwargs)
/srv/ddnmh01/limecms/nmh/nmh01/local/lib/python2.7/site-packages/mako/runtime.py, line 873:
_exec_template(inherit, lclcontext, args=args, kwargs=kwargs)
/srv/ddnmh01/limecms/nmh/nmh01/local/lib/python2.7/site-packages/mako/runtime.py, line 838:
**_kwargs_for_callable(callable_, data))
/srv/ddnmh01/limecms/nmh/nmh01/local/lib/python2.7/site-packages/mako/template.py, line 462:
return runtime._render(self, self.callable_, args, data)
/var/limecms/nmh/nmh01/nmh-inst-01/Products/LimeTemplate/LimeTemplate.py, line 704:
html = mytemplate.render(object=object, site=site, request=self.REQUEST, extra=extra.get('kwargs', None), **extra)