It's generally wrong to bid RKCB with a void because partner's response might be completely meaningless to you. Suppose on this hand he shows 1 keycard. It's more or less a coinflip that he has the ace of spades rather than the king of trumps. If you ask for the Q and he denies it, then what do you do? You'd look silly getting to slam missing the KQJ of trumps. If you just play straight blackwood, I guess this is fine, but when you ask for the number of kings partner has, again he could easily have the king of spades. The solution is to cuebid rather than ask for keycards. In this case you're interested in hearing about a ♦ cuebid and later about good trumps.