/**
     * Is the property true?
     * @param propertyKey The key of the property which is boolean type. (NotNull)
     * @return The determination, true or false. (if not found, exception)
     * @throws ConfigPropertyNotFoundException When the property is not found.
     */
    boolean is(String propertyKey);

    /**
     * Get the value for the key 'domain.title'. <br>