If you get autofilled and you can't play the role, please dodge.
I honestly don't feel like auto fill should be in the game. When a game is dependent on who got auto filled to a role they can't play and they play the game anyway, it just makes for a bad experience overall. This happens in not just diamond, but plat as well.
If you're one of the players that unfortunately ends up getting auto filled, please save yourself and the 4 other players on the team time by dodging the queue. It costs 3 LP and literally does not affect your MMR. It's a lot better than having to play something you have 0 proficiency at and losing MMR as well as wasting everyone else's time.
Sincerely, a player that wants to get out of P1 hell.