Refs #35381 -- Delegated ArrayField element prepping to base_field.get_db_prep_save.

Previously, ArrayField always used base_field.get_db_prep_value when saving,
which could differ from how base_field prepares data for save. This change
overrides ArrayField.get_db_prep_save to delegate to the base_field's
get_db_prep_save, ensuring elements like None in JSONField arrays are saved
correctly as SQL NULL instead of JSON null.

tests/postgres_tests/test_array.py

@@ -10,6 +10,7 @@ from django.core import checks, exceptions, serializers, validators
 from django.core.exceptions import FieldError
 from django.core.management import call_command
 from django.db import IntegrityError, connection, models
+from django.db.models import JSONNull
 from django.db.models.expressions import Exists, F, OuterRef, RawSQL, Value
 from django.db.models.functions import Cast, JSONObject, Upper
 from django.test import TransactionTestCase, override_settings, skipUnlessDBFeature
@@ -1577,3 +1578,29 @@ class TestAdminUtils(PostgreSQLTestCase):
             self.empty_value,
         )
         self.assertEqual(display_value, self.empty_value)
+
+
+class TestJSONFieldQuerying(PostgreSQLTestCase):
+    def test_saving_and_querying_for_sql_null(self):
+        obj = OtherTypesArrayModel.objects.create(json=[None, None])
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__isnull=True), [obj]
+        )
+
+    def test_saving_and_querying_for_json_null(self):
+        obj = OtherTypesArrayModel.objects.create(json=[JSONNull(), JSONNull()])
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1=JSONNull()), [obj]
+        )
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__isnull=True), []
+        )
+
+    def test_saving_and_querying_for_nested_json_nulls(self):
+        obj = OtherTypesArrayModel.objects.create(json=[[None, 1], [None, 2]])
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__0=None), [obj]
+        )
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__0__isnull=True), []
+        )