From c401be447d41f6e98418f6395195c1048cadb5d5 Mon Sep 17 00:00:00 2001
From: "T. Franzel" <tfranzel@users.noreply.github.com>
Date: Tue, 26 Dec 2023 15:33:42 +0100
Subject: [PATCH] add OAS 3.1 null translation case #1133

---
 drf_spectacular/plumbing.py |  2 ++
 tests/test_regressions.py   | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/drf_spectacular/plumbing.py b/drf_spectacular/plumbing.py
index c5a6a03b..f6c8d5c3 100644
--- a/drf_spectacular/plumbing.py
+++ b/drf_spectacular/plumbing.py
@@ -535,6 +535,8 @@ def append_meta(schema: _SchemaType, meta: _SchemaType) -> _SchemaType:
                 schema = {'oneOf': [schema, {'type': 'null'}]}
             elif len(schema) == 1 and 'oneOf' in schema:
                 schema['oneOf'].append({'type': 'null'})
+            elif not schema and not meta:
+                schema = {'oneOf': [{}, {'type': 'null'}]}
             else:
                 assert False, 'Invalid nullable case'  # pragma: no cover
 
diff --git a/tests/test_regressions.py b/tests/test_regressions.py
index 478c721e..a8188537 100644
--- a/tests/test_regressions.py
+++ b/tests/test_regressions.py
@@ -3260,3 +3260,38 @@ def view_func(request, format=None):
     assert get_request_schema(schema['paths']['/x/']['post']) == {
         '$ref': '#/components/schemas/Simple'
     }
+
+
+@mock.patch('drf_spectacular.settings.spectacular_settings.OAS_VERSION', '3.1.0')
+def test_basic_oas_3_1_nullable_cases(no_warnings, django_transforms):
+    class M14(models.Model):
+        field_json = models.JSONField(null=True)  # case 1
+
+    class XSerializer(serializers.ModelSerializer):
+
+        field_method_hint = serializers.SerializerMethodField()
+
+        def get_field_method_hint(self, obj) -> typing.Union[int, str, None]:  # case 2
+            pass  # pragma: no cover
+
+        class Meta:
+            fields = '__all__'
+            model = M14
+
+    class XViewset(viewsets.ReadOnlyModelViewSet):
+        serializer_class = XSerializer
+        queryset = M14.objects.none()
+
+    schema = generate_schema('m2', XViewset)
+    assert schema['components']['schemas']['X']['properties'] == {
+        'id': {'readOnly': True, 'type': 'integer'},
+        'field_json': {'oneOf': [{}, {'type': 'null'}]},
+        'field_method_hint': {
+            'oneOf': [
+                {'type': 'integer'},
+                {'type': 'string'},
+                {'type': 'null'}
+            ],
+            'readOnly': True
+        },
+    }