Is the variable empty (Null, or empty string), or the passed value ?
A variant value
The empty comparison value
mt_or_0(Null, 23) => True
mt_or_0("", 23) => True
mt_or_0("0", 23) => False
mt_or_0(0, 23) => False
mt_or_0(23, 23) => True
mt_or_0(False, 23) => False