* @param propertyKey The key of the property. (NotNull)
     * @return The value of found property. (NotNull: if not found, exception)
     * @throws ConfigPropertyNotFoundException When the property is not found.
     */
    String get(String propertyKey);

    /**
     * Is the property true?
     * @param propertyKey The key of the property which is boolean type. (NotNull)

    public static final String LABELS_LOGIN_UPDATE = "{labels.login.update}";

    /**
     * Assert the property is not null.
     * @param property The value of the property. (NotNull)
     */
    protected void assertPropertyNotNull(String property) {
        if (property == null) {
            String msg = "The argument 'property' for message should not be null.";