ASP.NET MVC: Posting JSON to Controller
I've got this in my controller:

        [HttpPost]
        public void UpdateLanguagePreference(string languageTag)
        {
            if (string.IsNullOrEmpty(languageTag))
            {
                throw new ArgumentNullException("languageTag");
            }

            ...
        }

And have this jQuery code POSTing to the controller:

               jQuery.ajax({
                    type: 'POST',
                    url: '/Config/UpdateLanguagePreference',
                    contentType: 'application/json; charset=utf-8',
                    data: '{ "languageTag": "' + selectedLanguage + '" }'
                });

When I try to the code, however, I get the error:

    Server Error in '/' Application.
    Value cannot be null.
    Parameter name: languageTag

What's the problem? Isn't this how to POST JSON to an MVC Controller? I can examine the POST using Fiddler and see that the request is correct. For some reason, `UpdateLanguagePreference()` is getting a null or empty string. 
ASP.NET MVC: Posting JSON to Controller
===

I've got this in my controller:

        [HttpPost]
        public void UpdateLanguagePreference(string languageTag)
        {
            if (string.IsNullOrEmpty(languageTag))
            {
                throw new ArgumentNullException("languageTag");
            }

            ...
        }

And have this jQuery code POSTing to the controller:

               jQuery.ajax({
                    type: 'POST',
                    url: '/Config/UpdateLanguagePreference',
                    contentType: 'application/json; charset=utf-8',
                    data: '{ "languageTag": "' + selectedLanguage + '" }'
                });

When I try to the code, however, I get the error:

    Server Error in '/' Application.
    Value cannot be null.
    Parameter name: languageTag

What's the problem? Isn't this how to POST JSON to an MVC Controller? I can examine the POST using Fiddler and see that the request is correct. For some reason, `UpdateLanguagePreference()` is getting a null or empty string. 