Return empty json on null in WebAPI

Question

Is it possible to return { } instead of null when webApi returns a null object? This, to prevent my user from getting errors while parsing the response. And to make the respon

Answer 1

Maybe better solution is using Custom Message Handler.

A delegating handler can also skip the inner handler and directly create the response.

Custom Message Handler:

public class NullJsonHandler : DelegatingHandler
    {
        protected override async Task SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {

            var updatedResponse = new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = null
            };

            var response = await base.SendAsync(request, cancellationToken);

            if (response.Content == null)
            {
                response.Content = new StringContent("{}");
            }

            else if (response.Content is ObjectContent)
            {

                var contents = await response.Content.ReadAsStringAsync();

                if (contents.Contains("null"))
                {
                    contents = contents.Replace("null", "{}");
                }

                updatedResponse.Content = new StringContent(contents,Encoding.UTF8,"application/json");

            }

            var tsc = new TaskCompletionSource();
            tsc.SetResult(updatedResponse);   
            return await tsc.Task;
        }
    }

Register the Handler:

In Global.asax file inside Application_Start() method register your Handler by adding below code.

GlobalConfiguration.Configuration.MessageHandlers.Add(new NullJsonHandler());

Now all the Asp.NET Web API Response which contains null will be replaced with empty Json body {}.

References:
- https://stackoverflow.com/a/22764608/2218697
- https://docs.microsoft.com/en-us/aspnet/web-api/overview/advanced/http-message-handlers