OpenAPI: only include non-empty required property. (#6851)

Closes #6834

rest_framework/schemas/openapi.py

@@ -381,10 +381,14 @@ class AutoSchema(ViewInspector):
             self._map_field_validators(field.validators, schema)
 
             properties[field.field_name] = schema
-        return {
-            'required': required,
-            'properties': properties,
+
+        result = {
+            'properties': properties
         }
+        if len(required) > 0:
+            result['required'] = required
+
+        return result
 
     def _map_field_validators(self, validators, schema):
         """
@@ -470,7 +474,8 @@ class AutoSchema(ViewInspector):
             for name, schema in item_schema['properties'].copy().items():
                 if 'writeOnly' in schema:
                     del item_schema['properties'][name]
-                    item_schema['required'] = [f for f in item_schema['required'] if f != name]
+                    if 'required' in item_schema:
+                        item_schema['required'] = [f for f in item_schema['required'] if f != name]
 
         if is_list_view(path, method, self.view):
             response_schema = {

tests/schemas/test_openapi.py

@@ -142,6 +142,32 @@ class TestOperationIntrospection(TestCase):
         assert request_body['content']['application/json']['schema']['required'] == ['text']
         assert list(request_body['content']['application/json']['schema']['properties'].keys()) == ['text']
 
+    def test_empty_required(self):
+        path = '/'
+        method = 'POST'
+
+        class Serializer(serializers.Serializer):
+            read_only = serializers.CharField(read_only=True)
+            write_only = serializers.CharField(write_only=True, required=False)
+
+        class View(generics.GenericAPIView):
+            serializer_class = Serializer
+
+        view = create_view(
+            View,
+            method,
+            create_request(path)
+        )
+        inspector = AutoSchema()
+        inspector.view = view
+
+        request_body = inspector._get_request_body(path, method)
+        # there should be no empty 'required' property, see #6834
+        assert 'required' not in request_body['content']['application/json']['schema']
+
+        for response in inspector._get_responses(path, method).values():
+            assert 'required' not in response['content']['application/json']['schema']
+
     def test_response_body_generation(self):
         path = '/'
         method = 'POST'