@Override
    public boolean isA(Type type) {
        if (!(type instanceof OptionalType)) {
            return false;
        }
        OptionalType other = ((OptionalType) type);
        return other.inner.isA(this.inner);
    }
The "optional" type, a container for a type that may or may not be present.
smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/evaluation/type/OptionalType.java