WebAPI controller that return void break iOS

[dicko2]

When a webapi controller returns void, aspnet make it return a 204 instead of 200. iOS/Safari treat this differently and prompt the user for a document download blocking off the website the instant the API method is called from ajax.

We should create a rule that forces all webapi controller methods to return data and not a void.

[Chrissx]

Only little concern about this the referrence that we need to add to "find" inherited members from ApiController/Controller. Should it be a new package beside Agoda.Analyzers.Web? The other parts looks easy to add I think.