导入带guid类型时报错

[nidapeng]

public class WeiChat_BrokerClient3 : WeiChat_WeChatWithNoKeyBase
{

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    /// <summary>
    ///   用户id
    /// </summary>
    [Display(Name = "用户ID")]
    public Guid userId { get; set; }

 。。。。。
}

}
执行的代码是
//导入数据

        var filePath = Path.Combine(Server.MapPath("~/upload"), "1.xlsx");

        var import = await Importer.Import<WeiChat_BrokerClient3>(filePath);
        import.ShouldNotBeNull();