SetValue test succeeds with my Period class but fails with my Name class

So my first TestMethod went through, as expected. I tested my SetValue method.

    p1 = new DateTimePeriod { From = DateTime.MinValue, To = DateTime.MaxValue };
    p2 = new DateTimePeriod { From = DateTime.MaxValue, To = DateTime.MinValue };

    [TestMethod]
    public void SetPeriodTest()
    {
        b.SetValue(ref p1, p2);
        Assert.AreEqual(DateTime.MaxValue, p1.From);
        Assert.AreEqual(DateTime.MinValue, p2.To);
    }

But the next test fails. Apparently x.AName, x.Valid and x.Id are null although I clearly set them the same way I set p1.From and p1.To. Why are these properties returning null?

    [TestMethod]
    public void SetNameTest()
    {
        var x = new Name { AName = "Jack", Valid = p1, Id = "123" };
        var y = new Name { AName = "John", Valid = p2, Id = "321" };
        b.SetValue(ref x, y);
        Assert.AreEqual("John", x.AName);
        Assert.AreEqual(p2, x.Valid);
        Assert.AreEqual("321", x.Id);
    }