Suppress properties with null value on ASP.NET Web API

In the WebApiConfig:

config.Formatters.JsonFormatter.SerializerSettings = 
                 new JsonSerializerSettings {NullValueHandling = NullValueHandling.Ignore};

Or, if you want more control, you can replace entire formatter:

var jsonformatter = new JsonMediaTypeFormatter
{
    SerializerSettings =
    {
        NullValueHandling = NullValueHandling.Ignore
    }
};

config.Formatters.RemoveAt(0);
config.Formatters.Insert(0, jsonformatter);

For ASP.NET Core 3.0, the ConfigureServices() method in Startup.cs code should contain:

services.AddControllers()
    .AddJsonOptions(options =>
    {
        options.JsonSerializerOptions.IgnoreNullValues = true;
    });

I ended up with this piece of code in the startup.cs file using ASP.NET5 1.0.0-beta7

services.AddMvc().AddJsonOptions(options =>
{
    options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;
});