[Fact]
        public void DisallowNull_04()
        {
            var source =
@"using System.Runtime.CompilerServices;
class Program
{
    static void F1([DisallowNull]int i) { }
    static void F2([DisallowNull]int? i) { }
    static void M1(int i1)
    {
        F1(i1);
        F2(i1);
    }
    static void M2(int? i2)
    {
        F2(i2); // I expected a warning here (jcouv)
        if (i2 == null) return;
        F2(i2);
    }
}";
            var comp = CreateCompilation(new[] { DisallowNullAttributeDefinition, source }, options: WithNonNullTypesTrue());
            comp.VerifyDiagnostics();
        }