public class Question
{
    [required]
    public string QuestionText { get; set; }

    [Range(1,5)]
    public int Difficulty { get; set; }        
}

具有以下验证代码

ICollection<ValidationResult> results = new List<ValidationResult>();
Question question = new Question();
ValidationContext ctx = new ValidationContext(question,null,null);
Validator.TryValidateObject(question,ctx,results);
// results.Length = 1

为什么Range属性不会在需要时创建验证错误(值显然为0)？