It seemed odd to me that their fail context didn't set 'err', but assumed it would be set by the origin of the jump. At least, I would have initialized 'err' to

It seemed odd to me that their fail context didn't set 'err', but assumed it would be set by the origin of the jump. At least, I would have initialized 'err' to a failure value, so that any mistake that led it not to be set would result in a valid error state.