Fixed crash deleting required schema parameter key on PATCH requests. (#6944)

Closes #6941

rest_framework/schemas/openapi.py

@@ -387,7 +387,7 @@ class AutoSchema(ViewInspector):
         result = {
             'properties': properties
         }
-        if len(required) > 0:
+        if required:
             result['required'] = required
 
         return result
@@ -463,7 +463,7 @@ class AutoSchema(ViewInspector):
         content = self._map_serializer(serializer)
         # No required fields for PATCH
         if method == 'PATCH':
-            del content['required']
+            content.pop('required', None)
         # No read_only fields for request.
         for name, schema in content['properties'].copy().items():
             if 'readOnly' in schema:

tests/schemas/test_openapi.py

@@ -169,6 +169,31 @@ class TestOperationIntrospection(TestCase):
         for response in inspector._get_responses(path, method).values():
             assert 'required' not in response['content']['application/json']['schema']
 
+    def test_empty_required_with_patch_method(self):
+        path = '/'
+        method = 'PATCH'
+
+        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'