Since the space bar doesn't do anything when Geralt is unarmed, I'd like to suggest to CDPR to allow rolling when Geralt is unarmed (e.g. sheathed weapon, or no weapons at all). Sometimes battles start right at the end of a cutscene where Geralt is surrounded and his enemies are already armed, and there are a couple of scenarios in the game where Geralt faces armed opponents with his fists.

Doesn't double-tapping the direction keys work?