Parameters binding removes whitespace

Describe the bug

Binding parameters of controller methods to HTTP request values e.g. using the [FromForm] attribute results in null value when the value contains whitespace only.

To Reproduce

[HttpPost]
public IActionResult Post([FromForm] string text = null) { ... }

POST http://localhost:53777/post HTTP/1.1
Content-Type: application/x-www-form-urlencoded

text=%E2%80%AF

(i.e. the value is U+202F Narrow No-Break Space)

Actual: The Post method is called with text being null.

Expected: The Post method is called with text being "\u202f", corresponding to the Request.Form["text"] value.

The same happens with mapping GET parameters and Request.Query["text"]. If this is by design, is there a way to turn it off?

Further technical details

.NET SDKs installed:
2.2.207 [C:\Program Files\dotnet\sdk]
5.0.200-preview.20614.14 [C:\Program Files\dotnet\sdk]

ASP.NET Core version: 2.2 Visual Studio 16.9.0 Preview 3.0

[pensono]

Just comparing to null would be enough, otherwise we would have the same problem with the empty string.

[pensono]

Note that the values present in ControllerBase.Request do contain whitespace as expected. It can be used as a workaround for this bug.

My controller looks something like this:

[HttpGet("myEndpoint")]
public async Task<ActionResult> GetEndpoint([FromQuery] string? paramWithWhitespace)
{
    // This treats whitespace correctly https://github.com/dotnet/aspnetcore/issues/29948
    paramWithWhitespace = Request.Query[nameof(paramWithWhitespace)];

    // ...
}

Example request URL: https://localhost:6670/myEndpoint?paramWithWhitespace=%20

Also, a related stack overflow: https://stackoverflow.com/questions/49797196/asp-net-space-in-query-parameter-value