Json.net sayes that json string is valid, but it's not

Question

I am trying to pars json string:

{"name":,"age":30,"car":null}

First problem occurs when I parse json string into token.

JToken token = JToken.Parse(json);

After pasing json string json token has additional curly bracers.

{{"name":,"age":30,"car":null}}

Could you tell me why?

Next problem occurs when I try yo deserialize json string into .net object.

JToken.Parse() adds undefined to the name property:

{{"name": undefined,"age":30,"car":null}}

And deserialization fails. I expect that it will add null to the name property so json string can be converted to the .net object without exception. But, it doesn't and I am getting exception:

Newtonsoft.Json.JsonReaderException: 'Unexpected character encountered while parsing value: u. Path 'name', line 2, position 11.' 

How can I successfully parse such json string so it could be safely converted to the .net object?

Here is class structure for json string:

public class User
    {
        public string name { get; set; }
        public int age { get; set; }
        public object car { get; set; }
    }