extend_schema with OpenApiResponse results in description: null in generated schema

[eviltwin]

Describe the bug
When using extend_schema to add examples to an endpoint, if you do not give a value for the OpenApiResponse's description parameter then it will produce a schema with description: null rather than description: ''. This is invalid according to the specification.

This prevents the schema from being used by openapi-python-client to generate client libraries.

I think this is because the default value in OpenApiResponse.__init__ is None when it should be ''.

Obviously, there is a workaround of simply providing description='' to OpenApiResponse (or, you know, an actual description).

To Reproduce

class WidgetViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows widgets to be viewed or edited.
    """

    queryset = Widget.objects.all()
    serializer_class = WidgetSerializer
    permission_classes = [permissions.IsAuthenticated]

    @extend_schema(
        responses={
            200: OpenApiResponse(
                response=WidgetSerializer,
                examples=[
                    OpenApiExample(
                        "Undamaged Widget",
                        value={
                            "is_damaged": False,
                            "damage_reason": "",
                        },
                    ),
                    OpenApiExample(
                        "Damaged Widget",
                        value={
                            "is_damaged": True,
                            "damage_reason": "Someone broke it.",
                        },
                    ),
                ],
            )
        }
    )
    def retrieve(self, request, *args, **kwargs):
        return super().retrieve(request, *args, **kwargs)
        

Expected behavior
The schema should contain description: '' when no description parameter is passed to OpenApiResponse, just like it does by default when not using extend_schema.

[tfranzel]

@eviltwin thx! yes, that was a momentary lapse in judgement that resulted in a regression. should be fixed now.

[eviltwin]

thanks! change looks like it will do the right thing so I'll close this :)