score:0

[fact]
public void getsum()
{
    var classes = new[]
    {
        new testclass {amount = null, id = 1},
        new testclass {amount = 1, id = 0}
    };

    var sum1 = classes.where(i => i.id > 1)
                      .select(i => i.amount)
                      .aggregate((double?)null, (a, b) => a.hasvalue && b.hasvalue ? a + b : a ?? b);
    var sum2 = classes.select(i => i.amount)
                      .aggregate((double?)null, (a, b) => a.hasvalue && b.hasvalue ? a + b : a ?? b);
    assert.null(sum1);
    assert.notnull(sum2);
}

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