FIX #4; Champion lock at start of turn

src/model/turn.py

@@ -189,7 +189,7 @@ class Turn(Serializable):
     async def start_turn(self) -> None:
         for c in self.player.board:
             if c.card_type == CardType.CHAMPION:
-                await self.lock_card(str(c.card_id))
+                await self.lock_card(str(c.uuid))
 
     def serialize(self):
         data = super().serialize() | {
@@ -211,6 +211,9 @@ class Turn(Serializable):
             return await self.player.put_on_stack_from_discard(str(card.uuid))
 
     async def stack_next_card_bought_check(self, card: Card) -> bool:
+        if card.cost is None:
+            print("You cannot buy a card that doesn't has any cost")
+            return False
 
         if self.gold_reserve < card.cost:
             print("Not enough gold to buy card!")