CraftMetaFirework: AssertionError -> IllegalArgumentException

src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaFirework.java

@@ -154,7 +154,7 @@ class CraftMetaFirework extends CraftMetaItem implements FireworkMeta {
             case BURST:
                 return 4;
             default:
-                throw new AssertionError(type);
+                throw new IllegalArgumentException("Unknown effect type " + type);
         }
     }
 
@@ -171,7 +171,7 @@ class CraftMetaFirework extends CraftMetaItem implements FireworkMeta {
             case 4:
                 return Type.BURST;
             default:
-                throw new AssertionError(nbt);
+                throw new IllegalArgumentException("Unknown effect type " + nbt);
         }
     }