Django 2で "does not appear to have any patterns in it" エラー

Django 2系で発生。

    raise ImproperlyConfigured(msg.format(name=self.urlconf_name))
django.core.exceptions.ImproperlyConfigured: The included URLconf '<module 'apps.aaaa.urls' from '/Users/aa/PycharmProjects/project1/apps/aaaa/urls.py'>' does not appear to have any patterns in it. If you see valid patterns in the file then the issue is probably caused by a circular import.

urls.py

urlpatterns = (
    # www.example.com/path/info/
    url(r'^accounts/', views.api1, name="api1")
)

tuple ( ) でurlpatternsを作って、要素数が1個だと、このエラーが発生するっぽい。

listにすると解決。

urlpatterns = [
    # www.example.com/path/info/
    url(r'^accounts/', views.api1, name="api1")
]

要素の末尾に
url(r'^accounts/', views.api1, name="api1"),
, をつけても直る。