So there's `undef` and `null`? I wonder if there's a popular language that made the same mistake you could have learnt from :-P
I thought that was clever given that tcl's reference counter was signed and it only uses positive values. So we made it unsigned and got the bit for free.
So yeah, there is some sloppiness there. Tcl tends to use "" as sort of a null or undef so lots of stuff just works but no promises on that.
This is sloppy simply because the Tcl die hards (are there any left?) refused to see the value of undef, a value for a variable that said there is no value. We used it all over the place, there clearly is value. They didn't see that, Little never got pushed back into the Tcl source base so Tcl never thought about undef.
It is what it is, we live in an imperfect world. I tried.