Fix mulligan with zero cards

forge-ai/src/main/java/forge/ai/ComputerUtil.java

@@ -2066,7 +2066,7 @@ public class ComputerUtil {
     // Computer mulligans if there are no cards with converted mana cost of 0 in its hand
     public static boolean wantMulligan(Player ai, int cardsToReturn) {
         final CardCollectionView handList = ai.getCardsIn(ZoneType.Hand);
-        return scoreHand(handList, ai, cardsToReturn) <= 0;
+        return !handList.isEmpty() && scoreHand(handList, ai, cardsToReturn) <= 0;
     }
 
     public static CardCollection getPartialParisCandidates(Player ai) {

forge-game/src/main/java/forge/game/card/CardFactory.java

@@ -116,7 +116,6 @@ public class CardFactory {
         //out.setFaceDown(in.isFaceDown());
 
         return out;
-
     }
 
     /**
@@ -740,7 +739,6 @@ public class CardFactory {
                 }
             }
 
-
             if (sa.hasParam("GainThisAbility") && (sa instanceof SpellAbility)) {
                 SpellAbility root = ((SpellAbility) sa).getRootAbility();
 

forge-game/src/main/java/forge/game/mulligan/AbstractMulligan.java

@@ -29,6 +29,7 @@ public abstract class AbstractMulligan {
 
     public void mulligan() {
         CardCollection toMulligan = new CardCollection(player.getCardsIn(ZoneType.Hand));
+        if (toMulligan.isEmpty()) return;
         revealPreMulligan(toMulligan);
         for (final Card c : toMulligan) {
             player.getGame().getAction().moveToLibrary(c, null);