You could use cidrmatch with the generic subnet 0.0.0.0/0. For IPv6 addresses you can use ::/0. Any valid IP address would return TRUE, anything else would return FALSE, as in the example below.
| makeresults | eval ip="10.0.1.8", validIP?=if(cidrmatch("0.0.0.0/0",ip) OR cidrmatch("::/0",ip), "YES", "NO")
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