As of this commit allowing for negative power, the `power` field has become type `Integer` allowing it to be null (by default). The `getPower()` method does not, however, check for its nullability and does an unboxing operation to return a primitive `int`. This can be quickly fixed with a ternary.

    @Override
    public int getPower() {
-        return this.power;
+        return hasPower() ? this.power : 0;
    }