From ef19aec2caab1ad246fd48ba1cf7c02e05706a5d Mon Sep 17 00:00:00 2001
From: kjpc-tech <kyle@kjpc.tech>
Date: Thu, 14 May 2020 16:56:21 -0600
Subject: [PATCH] [3.1.x] Fixed #31590 -- Fixed ModelAdmin.date_hierarchy crash
 with an empty QuerySet.

Regression in 55cdf6c52db07f29128741b8734a523ed042e465.

Backport of 099bce1bf0b9802b7159beb9260b9b9e344bf497 from master
---
 django/contrib/admin/templatetags/admin_list.py | 10 +++++-----
 tests/admin_views/tests.py                      |  5 +++++
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/django/contrib/admin/templatetags/admin_list.py b/django/contrib/admin/templatetags/admin_list.py
index 2b48f09f21..55565579ae 100644
--- a/django/contrib/admin/templatetags/admin_list.py
+++ b/django/contrib/admin/templatetags/admin_list.py
@@ -380,12 +380,12 @@ def date_hierarchy(cl):
             # select appropriate start level
             date_range = cl.queryset.aggregate(first=models.Min(field_name),
                                                last=models.Max(field_name))
-            if dates_or_datetimes == 'datetimes':
-                date_range = {
-                    k: timezone.localtime(v) if timezone.is_aware(v) else v
-                    for k, v in date_range.items()
-                }
             if date_range['first'] and date_range['last']:
+                if dates_or_datetimes == 'datetimes':
+                    date_range = {
+                        k: timezone.localtime(v) if timezone.is_aware(v) else v
+                        for k, v in date_range.items()
+                    }
                 if date_range['first'].year == date_range['last'].year:
                     year_lookup = date_range['first'].year
                     if date_range['first'].month == date_range['last'].month:
diff --git a/tests/admin_views/tests.py b/tests/admin_views/tests.py
index eb6f009f03..4d307486f1 100644
--- a/tests/admin_views/tests.py
+++ b/tests/admin_views/tests.py
@@ -969,6 +969,11 @@ class AdminViewBasicTest(AdminViewBasicTestCase):
         self.assertEqual(response.context['site_url'], '/my-site-url/')
         self.assertContains(response, '<a href="/my-site-url/">View site</a>')
 
+    def test_date_hierarchy_empty_queryset(self):
+        self.assertIs(Question.objects.exists(), False)
+        response = self.client.get(reverse('admin:admin_views_answer2_changelist'))
+        self.assertEqual(response.status_code, 200)
+
     @override_settings(TIME_ZONE='America/Sao_Paulo', USE_TZ=True)
     def test_date_hierarchy_timezone_dst(self):
         # This datetime doesn't exist in this timezone due to DST.