DiagnosticSuppressor doesn't suppress values passed as arguments

[manfred-brands]

If a nullable variable is asserted to be not null and then passed to a method that expects a non-nullable instance, the errors are not suppressed, even if the variable is assigned to a local variable first.

[Test]
public void TestPassDirectly()
{
    string? possibleNull = GetNext();
    Assert.That(possibleNull, Is.Not.Null);
    AssertEmpty((string)possibleNull);
}

[Test]
public void TestPassViaLocal()
{
    string? possibleNull = GetNext();
    Assert.That(possibleNull, Is.Not.Null);
    string s = (string)possibleNull;
    AssertEmpty(s);
}

private static string? GetNext() => string.Empty;

private static void AssertEmpty(string s) => Assert.That(s, Is.EqualTo(string.Empty));