Allow empty request body in PUT and POST HTTP requests in .NET Core Web API

When you have an API where the body is not optional or nullable like this

        [HttpPut("{postId}")]
        public async Task<IActionResult> Update(
            [FromRoute] string postId,
            [FromBody] UpdatePostRequest request)
        {
            // Logic to update post
            ...

            return NoContent();
        }

If a client sends a request to this endpoint without Content-Type and body, they would get this error

{
  "type": "https://tools.ietf.org/html/rfc9110#section-15.5.16",
  "title": "Unsupported Media Type",
  "status": 415,
  "traceId": "00-92b30b239eca44beb048a4923d145cfc-4a150c0e97824d78-00"
}

And if the request has Content-Type in the headers, then this error will be returned

{
  "type": "https://datatracker.ietf.org/doc/html/rfc9110#section-15.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "traceId": "00-ded02a7403fd42ca8880e92f6963fc10-5ec659fe255b420e-00",
  "errors": {
    "": [
      "A non-empty request body is required."
    ]
  }
}

If you want to validate whether the request is empty manually in the controller so you can return a custom response, you can do the following

        [HttpPut("{postId}")]
        public async Task<IActionResult> Update(
            [FromRoute] string postId,
            [FromBody(EmptyBodyBehavior = EmptyBodyBehavior.Allow)] UpdatePostRequest request)
        {
            if (request == null)
            {
                // return some custom response.
            }

            // Logic to update post
            ...

            return NoContent();
        }

You can also allow Empty body globally. In your startup class, add the following

services.AddMvc()
        .AddMvcOptions(o => o.AllowEmptyInputInBodyModelBinding = true);