Deserializing JSON when sometimes array and sometimes object

I'm having a bit of trouble deserializing data returned from Facebook using the JSON.NET libraries.

The JSON returned from just a simple wall post looks like:

{
    "attachment":{"description":""},
    "permalink":"http://www.facebook.com/permalink.php?story_fbid=123456789"
}

The JSON returned for a photo looks like:

"attachment":{
        "media":[
            {
                "href":"http://www.facebook.com/photo.php?fbid=12345",
                "alt":"",
                "type":"photo",
                "src":"http://photos-b.ak.fbcdn.net/hphotos-ak-ash1/12345_s.jpg",
                "photo":{"aid":"1234","pid":"1234","fbid":"1234","owner":"1234","index":"12","width":"720","height":"482"}}
        ],

Everything works great and I have no problems. I've now come across a simple wall post from a mobile client with the following JSON, and deserialization now fails with this one single post:

"attachment":
    {
        "media":{},
        "name":"",
        "caption":"",
        "description":"",
        "properties":{},
        "icon":"http://www.facebook.com/images/icons/mobile_app.gif",
        "fb_object_type":""
    },
"permalink":"http://www.facebook.com/1234"

Here is the class I am deserializing as:

public class FacebookAttachment
    {
        public string Name { get; set; }
        public string Description { get; set; }
        public string Href { get; set; }
        public FacebookPostType Fb_Object_Type { get; set; }
        public string Fb_Object_Id { get; set; }

        [JsonConverter(typeof(FacebookMediaJsonConverter))]
        public List<FacebookMedia> { get; set; }

        public string Permalink { get; set; }
    }

Without using the FacebookMediaJsonConverter, I get an error: Cannot deserialize JSON object into type 'System.Collections.Generic.List`1[FacebookMedia]'. which makes sense, since in