Description in Response cannot be null #3069

var doc = new OpenApiDocument
{
    Paths = new OpenApiPaths
    {
        ["/example"] = new OpenApiPathItem
        {
            Operations = new Dictionary<HttpMethod, OpenApiOperation>
            {
                [HttpMethod.Get] = new OpenApiOperation
                {
                    Responses = new OpenApiResponses
                    {
                        ["200"] = new OpenApiResponse
                        {
                            // No description
                        }
                    }
                }
            }
        }
    }
};

using var stringWriter = new StringWriter();
doc.SerializeAs(OpenApiSpecVersion.OpenApi3_0, new OpenApiJsonWriter(stringWriter));
var result = stringWriter.ToString();