@seancorfield Really weird. Here’s the same, running on a fresh REPL: http://eneroth.com/clojure-slack/proto-repl-group-by-2.png

As soon as nil is in there, it wonks out. Remove nil, and presto: http://eneroth.com/clojure-slack/proto-repl-group-by-3.png

@henrik Never seen anything like that 👀