Pop up an error when invoking (POST) application method with an empty payload

[v-mengwe]

OS: All
Build Version: 20200902.2

Repro Steps:

1. Create a new .NET Web API application by "dotnet new webapi --no-https --name netwebapp".
2. Open the application in VS Code --> Select "Dapr: Scaffold Dapr Tasks" from Command Palette --> Select ".NET Core Launch (web)" when asked to select a configuration --> Enter an application ID --> Enter an application port.
3. Add the following within the class definition:

[HttpPost]
	public ActionResult Post([FromBody] object body)
	{
              return new JsonResult(body);
        }

4. Debug with ".NET Core Launch (web) with Dapr".
5. Right click the running application --> Select "Invoke (POST) Application Method" --> Enter "WeatherForecast" --> Enter an empty payload.
6. Check the result.

Expect:
The method was invoked and succeeded.

Actual:
Pop up an error.

More Info:

1. This issue also reproduces for node.js project.
2. This issue doesn't reproduce when publishing message to application with an empty payload.

[philliphoff]

It looks like we're not handling empty payloads properly in the case of post/publish, though it happens to work for publish. I'll create a PR for a fix. Note, however, that you might still get an error response from the server (400 or 415) if the server expects a valid (i.e. non-null) payload (which ASP.NET does, when using the [FromBody] attribute.

[v-mengwe]

Got it, thanks for your sharing.