Fixed #21530 -- Prevent AttributeError in default URLconf detection code.

Thanks to @dmyerscoug for the report and original patch
and to @alasdairnicol for the added tests.

django/views/debug.py

@@ -483,7 +483,7 @@ def technical_404_response(request, exception):
             or (request.path == '/'
                 and len(tried) == 1             # default URLconf
                 and len(tried[0]) == 1
-                and tried[0][0].app_name == tried[0][0].namespace == 'admin')):
+                and getattr(tried[0][0], 'app_name', '') == getattr(tried[0][0], 'namespace', '') == 'admin')):
             return default_urlconf(request)
 
     urlconf = getattr(request, 'urlconf', settings.ROOT_URLCONF)

tests/view_tests/default_urls.py

+from django.conf.urls import patterns, include, url
+
+from django.contrib import admin
+
+urlpatterns = patterns('',
+    # This is the same as in the default project template
+    url(r'^admin/', include(admin.site.urls)),
+)

tests/view_tests/regression_21530_urls.py

+from django.conf.urls import patterns, url
+
+urlpatterns = patterns('',
+    url(r'^index/$', 'view_tests.views.index_page', name='index'),
+)

tests/view_tests/tests/test_debug.py

@@ -139,6 +139,35 @@ class DebugViewTests(TestCase):
         """
         self.assertRaises(TemplateDoesNotExist, self.client.get, '/render_no_template/')
 
+    @override_settings(ROOT_URLCONF='view_tests.default_urls')
+    def test_default_urlconf_template(self):
+        """
+        Make sure that the default urlconf template is shown shown instead
+        of the technical 404 page, if the user has not altered their
+        url conf yet.
+        """
+        response = self.client.get('/')
+        self.assertContains(
+            response,
+            "<h2>Congratulations on your first Django-powered page.</h2>"
+        )
+
+    @override_settings(ROOT_URLCONF='view_tests.regression_21530_urls')
+    def test_regression_21530(self):
+        """
+        Regression test for bug #21530.
+
+        If the admin app include is replaced with exactly one url
+        pattern, then the technical 404 template should be displayed.
+
+        The bug here was that an AttributeError caused a 500 response.
+        """
+        response = self.client.get('/')
+        self.assertContains(
+            response,
+            "Page not found <span>(404)</span>",
+            status_code=404
+        )
 
 class ExceptionReporterTests(TestCase):
     rf = RequestFactory()