转换枚举？诠释？使用反射时失败

使用int?转换成功。
使用反射进行转换时失败。
如何使用反射将值成功分配enum?给属性int?？

static void Main(string[] args)
{
    Dc dc = new Dc { Solution = Solution.Upgrade };

    Model model = new Model {  };

    //assign by reflection
    var psolution = model.GetType().GetProperty("Solution");
    //psolution.SetValue(model, dc.Solution); //this fail
    model.Solution = (int?)dc.Solution; //this success
    psolution.SetValue(model, Convert.ChangeType(dc.Solution, psolution.PropertyType)); //this fail
}

class Dc
{
    public Solution? Solution { get; set; }
}

class Model
{
    public int? Solution { get; set; }
}

enum Solution
{
    Upgrade = 1,
    Discard = 2,
}