old_contents: from django.conf import settings
  from django.core.exceptions import ImproperlyConfigured
  
  _reqs = ('django.contrib.auth', 'django.contrib.sessions')
  if getattr(settings, 'NEXUS_SKIP_INSTALLED_APPS_REQUIREMENTS', False):
      _reqs = ()
  for r in _reqs:
      if r not in settings.INSTALLED_APPS:
          raise ImproperlyConfigured("Put '%s' in your "
              "INSTALLED_APPS setting in order to use the nexus application." % r)
  
  # XXX but we needed registered nexus modules to update
  # STATICFILES_DIRS setting for collectstatic command
  __import__(settings.ROOT_URLCONF)
  
new_contents: from django.conf import settings
  from django.core.exceptions import ImproperlyConfigured
  
  _reqs = ('django.contrib.auth', 'django.contrib.sessions')
  if getattr(settings, 'NEXUS_SKIP_INSTALLED_APPS_REQUIREMENTS', False):
      _reqs = ()
  for r in _reqs:
      if r not in settings.INSTALLED_APPS:
          raise ImproperlyConfigured("Put '%s' in your "
              "INSTALLED_APPS setting in order to use the nexus application." % r)
  
subject: remove url import in models