Why does POST without parameters not return JSON - asp.net-mvc

Question

I have a controller method
[HttpPost]
public ActionResult GetUserData()
{
return Json(GetCurrentUser());
}
I'm calling it $.ajax() through a method like this:
ServerCall: function (method, args, callback) {
$.ajax({
type: 'POST',
url: method,
data: JSON.stringify(args),
contentType: 'application/json;charset=utf8',
dataType: 'json',
success: function (result) {
if (callback) {
callback(result);
}
},
error: function (err) {
}
});
}
with the call being:
ServerCall('GetUserData', null, function(data){
});
As it is, when I make this call, $.ajax returns with success, but 'data' is null. Debugging, responseText is empty. On the server side, GetUserData is called, and it is returning a properly formatted Json object (I've gone so far as to create my own JSON ActionResult and verified that data is indeed being written to the response stream.
If I add a dummy parameter to the server side method:
[HttpPost]
public ActionResult GetUserData(string temp)
{
return Json(GetCurrentUser));
}
everything works perfectly. Browser is IE8. My question is, can anyone explain why this is happening?
UPDATE:
Note workaround solution below: I'd still be interested in knowing the root cause.

Answer 1

No repro.
Controller:
public class HomeController : Controller
{
public ActionResult Index()
{
return View();
}
[HttpPost]
public ActionResult GetUserData()
{
return Json(new { foo = "bar" });
}
}
Index.cshtml view:
<script type="text/javascript">
var serverCall = function (method, args, callback) {
$.ajax({
type: 'POST',
url: method,
data: JSON.stringify(args),
contentType: 'application/json;charset=utf8',
dataType: 'json',
success: function (result) {
if (callback) {
callback(result);
}
},
error: function (err) {
}
});
};
serverCall('#Url.Action("GetUserData")', null, function (data) {
alert(data.foo);
});
</script>
result: 'bar' is alerted (as expected).

Answer 2

I was able to reproduce using Darin's code in IE8. While I don't know the root cause, I think it has something to do with how IE8 JSON.stringify handles null. Changing
data: JSON.stringify(args)
to
data: args ? JSON.stringify(args) : null
fixed the problem.
Note, the problem is intermittent - I was seeing failures in about one out of every ten calls. With the change, over 100 tests, the failure rate was zero.