Refs #28211 -- Added a test for ANDing empty Q()'s.

This test passes to due some logic in Node.add().

tests/queries/test_q.py

@@ -3,6 +3,14 @@ from django.test import SimpleTestCase
 
 
 class QTests(SimpleTestCase):
+    def test_combine_and_empty(self):
+        q = Q(x=1)
+        self.assertEqual(q & Q(), q)
+        self.assertEqual(Q() & q, q)
+
+    def test_combine_and_both_empty(self):
+        self.assertEqual(Q() & Q(), Q())
+
     def test_deconstruct(self):
         q = Q(price__gt=F('discounted_price'))
         path, args, kwargs = q.deconstruct()