`NotSupportedException` with primitives other than `bool` and `int`

[John-Leitch]

XUnit throws a NotSupportedException in some cases when primitives other than bool and int are used. This is especially confusing when encountered from VS test explorer because little context is available.

Exception

Repro

namespace TestProject1
{
    public class UnitTest1
    {
        [Theory, CombinatorialData]
        public void Test1(uint test)
        {
            var prim = typeof(StringComparison).IsPrimitive;
        }
    }
}