Linq：整数之和

我正进入（状态 ”不能将 null 值分配给 System.Int32 类型的成员，该类型是不可为 null 的值类型“当执行我的空语句的 Sum() 时。 ResultView 工作正常，但是

var r = from v in DataContext.Visits
        join bs in DataContext.BaseContents on v.BaseContentID equals bs.Id
        where (bs.CreatedBy == userId) && (v.DateVisited.Year == workDate.Year) &&
        (v.DateVisited.Month == workDate.Month) && (v.DateVisited.Day == workDate.Day) &&
        (v.IsPreviewed == false) && (bs.ProfileProjectId != null)
        select v;

int? number = r.Sum( v => v.Counter);

either

var r = from v in DataContext.Visits
        join bs in DataContext.BaseContents on v.BaseContentID equals bs.Id
        where (bs.CreatedBy == userId) && (v.DateVisited.Year == workDate.Year) &&
        (v.DateVisited.Month == workDate.Month) && (v.DateVisited.Day == workDate.Day) &&
        (v.IsPreviewed == false) && (bs.ProfileProjectId != null)
        select v.Counter;

int? number = r.Sum(v);

因同样的异常而失败。

尝试这个 （updated):

int number = r.Sum(v => (int?)v.Counter) ?? 0;