1NT is 15-17, 2♥ is transfer, North´s first pass denies ♠ support, 4♦ is a cuebid and 5♥ is NOT Exclusion Blackwood (we do not play this convention), but promises a void. Please apportion the blame.
You can blame the partnership for not having the Exclusion Blackwood agreement, but that is not the issue here.
Benefits include:
Plus... it's free!