>But only variants can be null or empty...

That's true, only Variants can be Null (Null is a state of Variant); however, Empty is translated to whatever default value makes sense for some of the (non-Object, non-user-defined) data types:

    Dim s As String, d As Date, x As Single, y As Double, i As Integer
    s = Empty: d = Empty: x = Empty: y = Empty: i = Empty
    Debug.Print s, d, x, y, i

(The above compiles and runs, and - no surprise - numerics are made zero, and string made "".)

>I'm sure someone has complained about Oracle's idea that empty strings are null values.

I have certainly complained about that: I mean, what's not to love about conflating "this field intentionally left blank" with "no certain value could be obtained for this field"? /s

>...a rant about how nulls are a terrible offense against the true relational model...

By way of Wikipedia, found this: https://www.dcs.warwick.ac.uk/~hugh/TTM/TTM-TheAskewWall-pri.... A fine read. I am left wondering about how OUTER JOINs would be handled without NULLs. I am now also wondering if it was OUTER JOINs that made NULLs seem necessary.