The 1st part of this thread is in the 2020-12.1 announcement thread (
http://www.kara-moon.com/forum/index.php?topic=8607.0). I'm re-starting it here 'cause the topic really doesn't belong where it was (and still is because I don't know how to move messages).
The upshot is that sciurius has written a neat little patch which permits default NULL or empty arguments in functions. And, that really is neat. I've done a few tests with the new code and it seems to work just fine!
I even tried to create a function with multiple arguments (Defcall Foo arg1,arg2,arg3...) and assign null/empty values to them. Works like a charm.
Now, I need to explain this is the the docs