Coming back to this problem...
Error: Undefined operator NIL in form (NIL (CL-POSTGRES:EXEC-QUERY *DATABASE* "select * from table1;" (QUOTE POSTMODERN::SYMBOL-PLIST-ROW-READER)))
Last night I suddenly realized that this is a bug that was fixed a long time ago [1]. Get the current code from git, and it'll work. I should probably do a release again sometime soon.
[1]: https://github.com/marijnh/Postmodern/commit/1627b8a8f8d19181112ba9d6b9eb544...