revset: prevent crash caused by empty group expression while optimizing "or" An empty group expression "()" generates None in AST, so it should be tested before destructuring a tuple. "A | ()" is still evaluated to an error because I'm not sure whether "()" represents an empty set or an empty expression (= a unit value). They are identical in "or" operation, but they should be evaluated differently in "and" operation. expression empty set unit value ---------- --------- ---------- () {} A A & () {} A A | () A A