@Override
    public BooleanType expectBooleanType() throws InnerParseError {
        throw new InnerParseError(String.format("Expected boolean but found %s. hint: use `isSet` to convert "
                + "OptionalType[BooleanType] to bool", this));
    }
Gets the optional's contained value.

@return the optional's value.
smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/evaluation/type/OptionalType.java