How to pass null in body to endpoint within asp.net core 3.1

Question

I have the following action within an asp.net core 3.1 controller

[ApiController]
[Route("example")]
public class MyExampleController : ControllerBase
{
    [HttpPost("{id}/value")]
    public async Task<IActionResult> Post(string id, [FromBody] int? value)
      => Task.FromResult(Ok());
}

This works fine if I post a body value of int (for example: 1, 2, etc...)

However, I can't find a way to get a null value passed in.

If I pass in an empty body or null body I get a status code of 400 returned with a validation message of A non-empty request body is required. returned.

I've also tried to change the value parameter to be an optional argument with a default value of null:

public async Task<IActionResult> Post(string id, [FromBody] int? value = null)

How do I pass in null to this action?

Answer 1

Finally figured this out, big thanks to @Nkosi and @KirkLarkin helping fault find this.

Within the Startup.cs when configuring the controllers into the container we just need to alter the default mvc options to AllowEmptyInputInBodyModelBinding

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers(x => x.AllowEmptyInputInBodyModelBinding = true);
}

This way we can pass in null into the body of the post and it works perfectly fine. It also still applies the normal model validation via the attributes without having to check the ModelState manually:

public async Task<IActionResult> Post(string id,
        [FromBody][Range(1, int.MaxValue, ErrorMessage = "Please enter a value bigger than 1")]
        int? value = null)