Myself & P play 3♣ over 2NT is singleton ♠ (3 ♦ is singleton ♥) reasoning is after 2NT (20-22 pts must be 4333 for our system any other low 20 count we open 2♣ and rebid 2NT) we find that keeping the ♥ & ♠ for natural bids wastes far less space, and (lets be honest) most times opposite 20-22 flat with any 4-9 pt hand you'd prob want to be in 3NT anyway, with 10 plus (as in this case) you'd be investigating slam or looking to escape in minor game so why not get lots of bids off your chest with just one ! There is always pass available for minimum hands. So 2NT-3♣-3NT is don't worry about ♠ leave me in it unless you have a very good reason, 2NT-3♣-3♥ means 4♥and semi-stop in ♠ and can be passed or raised (with 4), or 3NT if singleton ♠ is honour card or /4♣/♦ with 5 card minor, and 2NT-3♣-3♠ is pick a minor level dependent on point count, 0-4 4 level 5-9 5 level with 3NT still available as slam interest in minor.