fix the TeamClient.AddMembership(..) call

[davidalpert]

While exploring some organizational automation with octokit.net I discovered that the TeamClient.AddMembership(..) call passes a null value into a parameter of ApiConnection.Put(..) that fails on an Octokit.Ensure.ArgumentNotNull(..) call.

The GitHub API 3.0 Team docs state that the correct way to call the Add Team Member endpoint is to essentially pass an empty body:

Note that you’ll need to set Content-Length to zero when calling out to this endpoint. For more information, see “HTTP verbs.”

• Add Team Member API docs

My proposed fix (that I will submit shortly in this PR) is to have ApiConnection.Put(..) check for a null body and respond by setting the Content-Length header to zero as instructed, if that is possible, rather than throwing an ArgumentNullExceptionValue.

Todo

• vet the design approach;
• configure the underlying Connection object to add the Content-Length header when the body is null
• removed the Content-Length header as that generated a System.InvalidOperationException: Misused header name.
• confirmed worked for my use case, used octokit to add users to a team;

[haacked]

Rather than accepting a null value, I wonder if we should have a special value. For example, we could have a static ApiConnection.EmptyBody property that's just an empty object and use that for cases when you're supposed to pass in an empty body. I try and avoid overloading null like this because it's hard to determine if you passed null as a mistake or intentionally.

Also, what happens if you just pass in new object() right now as the data argument. Does that do the right thing today?

[davidalpert]

@haacked tried your suggestion of an Empty static instead of null; moved it to it's own class to avoid coupling Connection to depend on ApiConnection while ApiConnection depends on IConnection.

Take a look. All tests pass. Ran .\build FixProjects to add ResponseBody.cs to all projects. And it fixed my use case. 👍

[shiftkey]

@davidalpert thanks for finding this and fixing it!