[Solved]-How to return null in a GroupBy statement when one of the values in the non-key column contains null?-LINQ,C#

you can accomplish this using linq's any method:

var query = toienumerable.groupby(c => c.country).select(r =>
{
    bool somewithnogrades = r.any(i => i.grade == null);

    return new
    {
        r.key,
        sumgrade = !somewithnogrades ? r.sum(f => f.grade) : null
    };
});