Optional body parameters no longer work since upgrading to .NET Core 2.0

[ben-foster-cko]

I have an action filter that automatically checks ModelState and returns 400 if it's not valid.

We have a few actions that have optional body parameters, for example:

        // POST api/values
        [HttpPost]
        public IActionResult Post([FromBody]SomeClass request = null)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            return Ok();
        }

Specifying the default value of null used to be enough to mark them as optional. Since upgrading to ASP.NET Core 2.0 I get the following response:

{
  "": [
    "A non-empty request body is required."
  ]
}

[ben-foster-cko]

It looks like the null handling behavior was changed in this PR.

There is a new option AllowEmptyInputInBodyModelBinding that is false by default. If you want to handle the null values yourself you'll need to set this to true.

[hmvs]

Would be nice to have something like [FromBody(AllowNull=true)] instead of having this behavior for all the methods.