创建隐藏敏感信息的自定义JSON转换器

我正在编写一个自定义JSON转换器,它将序列化一个对象并屏蔽包含一些敏感信息的某些字段。我已经创建了转换器,但是当我使用转换器序列化对象时,得到了一个空字符串。有人能告诉我我做错了什么吗?

public class Student
{
    public string Name { get; set; }

    public string Phone { get; set; }
}

class StudentJsonConverter : JsonConverter
{
    /// <inheritdoc />
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        if (value is Student student)
        {
            student.Phone = MaskString(student.Phone);
        }

        writer.WriteStartObject();
        serializer.Serialize(writer, value);
        writer.WriteEndObject();
    }

    /// <inheritdoc />
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    /// <inheritdoc />
    public override bool CanConvert(Type objectType) => typeof(Student) == objectType;

    private static string MaskString(string sensitiveInformation) => string.IsNullOrWhiteSpace(sensitiveInformation) ? null : new string('*', sensitiveInformation.Length);
}

在这里我使用它:

    JsonSerializerSettings settings = new JsonSerializerSettings();
    settings.Converters.Add(new StudentJsonConverter());
    settings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
    var student = new Student { Name = "name", Phone = "1234" };

    var serializedString = JsonConvert.SerializeObject(student, settings);

    Console.WriteLine(serializedString);

但我总是得到一个空字符串。