[4.1.x] Fixed #33996 -- Fixed CheckConstraint validation on NULL values.

Bug in 667105877e6723c6985399803a364848891513cc.

Thanks James Beith for the report.

Backport of e14d08cd894e9d91cb5d9f44ba7532c1a223f458 from main

2 files changed, 19 insertions, 4 deletions

diff --git a/tests/constraints/tests.py b/tests/constraints/tests.py
index d4054dfd77..5a498f0d73 100644
--- a/tests/constraints/tests.py
+++ b/tests/constraints/tests.py
@@ -6,7 +6,7 @@ from django.db.models import F
 from django.db.models.constraints import BaseConstraint
 from django.db.models.functions import Lower
 from django.db.transaction import atomic
-from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
+from django.test import SimpleTestCase, TestCase, skipIfDBFeature, skipUnlessDBFeature
 
 from .models import (
     ChildModel,
@@ -234,6 +234,23 @@ class CheckConstraintTests(TestCase):
         constraint.validate(Product, Product(price=501, discounted_price=5))
         constraint.validate(Product, Product(price=499, discounted_price=5))
 
+    @skipUnlessDBFeature("supports_comparing_boolean_expr")
+    def test_validate_nullable_field_with_none(self):
+        # Nullable fields should be considered valid on None values.
+        constraint = models.CheckConstraint(
+            check=models.Q(price__gte=0),
+            name="positive_price",
+        )
+        constraint.validate(Product, Product())
+
+    @skipIfDBFeature("supports_comparing_boolean_expr")
+    def test_validate_nullable_field_with_isnull(self):
+        constraint = models.CheckConstraint(
+            check=models.Q(price__gte=0) | models.Q(price__isnull=True),
+            name="positive_price",
+        )
+        constraint.validate(Product, Product())
+
 
 class UniqueConstraintTests(TestCase):
     @classmethod
diff --git a/tests/postgres_tests/test_constraints.py b/tests/postgres_tests/test_constraints.py
index 2850d0eb3d..74c07e4fab 100644
--- a/tests/postgres_tests/test_constraints.py
+++ b/tests/postgres_tests/test_constraints.py
@@ -146,9 +146,7 @@ class SchemaTests(PostgreSQLTestCase):
             check=Q(ints__startswith__gte=0),
             name="ints_positive_range",
         )
-        msg = f"Constraint “{constraint.name}” is violated."
-        with self.assertRaisesMessage(ValidationError, msg):
-            constraint.validate(RangesModel, RangesModel())
+        constraint.validate(RangesModel, RangesModel())
 
     def test_opclass(self):
         constraint = UniqueConstraint(