NancyFX Error handling. The OnError, does not return anything in the message body. What am I doing wrong??

gistfile1.cs

public class Bootstrapper : DefaultNancyBootstrapper
{
    protected override void RequestStartup(TinyIoCContainer requestContainer, IPipelines pipelines, NancyContext context)
    {
        pipelines.OnError += (ctx, ex) =>
        {
            return ErrorResponse.FromException(ex);
        };

        base.RequestStartup(requestContainer, pipelines, context);
    }
}

public class ErrorResponse : JsonResponse
{
    readonly Error error;

    private ErrorResponse(Error error) : base(error, new CustomJsonSerializer())
    {
        this.error = error;
    }

    public string ErrorMessage { get { return error.ErrorMessage; } }
    public string FullException { get { return error.FullException; } }
    public string[] Errors { get { return error.Errors; } }
    
    public static ErrorResponse FromException(Exception ex)
    {
        var statusCode = HttpStatusCode.InternalServerError;
        var error = new Error { ErrorMessage = ex.Message, FullException = ex.ToString() };


        var response = new ErrorResponse(error);
        response.StatusCode = statusCode;
        return response;
    }

    class Error
    {
        public string ErrorMessage { get; set; }

        [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
        public string FullException { get; set; }

        [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
        public string[] Errors { get; set; }
    }
}

public class CustomJsonSerializer : ISerializer
{
    public CustomJsonSerializer()
    {
        //this.ContractResolver = new CamelCasePropertyNamesContractResolver();
        //this.Formatting = Formatting.Indented;
    }

    public bool CanSerialize(string contentType)
    {
        //if (contentType == "application/json")
        //    return false;
        //if (contentType == "text/json")
        //    return false;
        //if (contentType == "text/html")
        //    return true;
        //return false;
        return true;
    }

    public IEnumerable<string> Extensions
    {
        get { throw new NotImplementedException(); }
    }

    public void Serialize<TModel>(string contentType, TModel model, Stream outputStream)
    {
        
    }
}

The issue was the the "CustomJsonSerializer.Serialize()" was not configured. So I'm dumb.
To resolve, instead of "private ErrorResponse(Error error) : base(error, new CustomJsonSerializer())", I just changed it to "DefaultJsonSerializer()"