[postmodern-devel] :IN/:NOT-IN on an empty :SET always results in :NULL

[Marijn Haverbeke]

Hi J.P.,

The (NULL) thing is a bit of a cop-out on my part since I, too,
couldn't figure out how to properly represent the empty set. I'd be
okay with just rigging :in and :not-in to check their rhs for nil and
expand to a boolean — people who do :null in {} are just asking for it
— but if you come up with a better approach let me know. Have you
investigated how do other SQL-generation engines deal with this icky
corner case?

Best,
Marijn