Avoid introducing an invalid creature type

forge-game/src/main/java/forge/game/ability/effects/ChooseTypeEffect.java

@@ -109,8 +109,9 @@ public class ChooseTypeEffect extends SpellAbilityEffect {
         //loop through sorted list and move each type to the front of the validTypes collection
         for (Entry<String, Integer> entry : sortedList) {
             String type = entry.getKey();
-            validTypes.remove(type);
+            if (validTypes.remove(type)) { //ensure an invalid type isn't introduced
                 validTypes.add(0, type);
             }
         }
     }
+}